She had no room for error. The engines were already fired up and Jackie Corin had 36 hours to bus 100 Parkland survivors 900 miles round-trip to Tallahassee, just six days after the shooting at Marjory Stoneman Douglas High School on February 14. Most of the kids had come to her mandatory meeting the previous night from funerals. In Tallahassee, they hoped to extract unlikely promises of new gun regulations from a state legislature controlled by Republicans. They were already in week six of Florida’s eight-week annual legislative session, and a bill hadn’t even been drafted. “We have about 10 days to craft really important legislation,” state representative Kristin Jacobs told me. “Because it’s a whole year before the legislature comes back together, and the momentum will be completely lost.” Even if they somehow struck a deal, the bill would go to Governor Rick Scott, a Second Amendment warrior with an A-plus N.R.A. rating.

Jackie had dreamed up, organized, and set the mission in motion over the weekend, working with her state senator to feed, house, transport, and chaperone the hundred minors, coax top officials to meet with them, and fund the whole undertaking. Despite the odds, everything had gone smoothly—until now. It was Tuesday afternoon, and Jackie’s recruits crammed the parking lot of Publix supermarket (“the one near the Walmart,” Jackie had clarified at the meeting), each holding two different releases signed by their parents. Three jumbo coach buses rumbled noisily, ready to roll. The press had appeared en masse, nearly outnumbering the students, and a news chopper buzzed overhead. The eight-hour journey itself was now a media spectacle, leading national newscasts, and the governor had agreed to meet. But a slew of last-minute glitches delayed their departure by nearly an hour. That’s when one of the bus drivers demanded that Jackie pay for his Tallahassee hotel room. “He got out of the bus and started walking away,” Jackie told me later. “I was a mess, I was crying. I kind of had a breakdown. ‘I have so much pressure on my shoulders—you cannot be doing this!’ ” She agreed to pay, and he took the wheel.

I’ve spent six months covering Jackie, who is one of the lead organizers for March for Our Lives (MFOL). I have seen her stressed and overloaded, bending but never breaking. During the Tallahassee trip, she exuded a steadfast calm. Students requested last-minute reassignments to sit with friends. “No,” she said sternly. “Get on your bus.” A school-board member agreed to chaperone, but kept chatting with me after the buses were loaded. Jackie whisked by, addressing another obstacle. “No more interviews,” she whispered, without looking up. The school-board member sheepishly turned to find his seat. She was never mean, just firm.

Jaclyn Corin, more comfortable as Jackie, is a petite blond teenager with fair skin, flowing hair, and a soprano voice that doesn’t carry in crowds. But she has a presence—and relentless tenacity. Jackie was elected freshman-class vice president, and president of her sophomore, junior, and now senior classes. She knows how to get things done.

I met her dad, Paul, in the Publix parking lot, as he watched in disbelief as Jackie managed the chaos. She’s always been a go-getter, he said, active in school leadership since middle school. But this? He could never imagine this. “I’m in awe,” he said. “Of my own daughter. I want to take her when she gets back to get her DNA tested, because I saw her come out of my wife, but I’m not sure I could produce this.”

Jackie Corin helped create #NeverAgainMSD, which evolved into MFOL. She will never command a stage like Emma González, match the fire of David Hogg’s Twitter feed, or keep the faithful giggling like Cameron Kasky, who delighted in telling reporters that he thought up the name #NeverAgain while sitting on the toilet in his Ghostbusters pajamas. But Jackie is a natural implementer and a driving force behind the scenes.

In its effort to make gun control a priority for midterm voters, MFOL has mobilized on two fronts: inspiring a massive following, and then building a network across thousands of high schools and colleges to drive young people to the polls. The first half was widely publicized—Emma alone has 1.6 million Twitter followers. But while she, David, and several others light up the Internet, Jackie tackles the logistics. Movements are born from hope, but they are built brick by brick. That’s Jackie’s department. If these kids rock the vote on Election Day, Jackie Corin will be a crucial reason why.

The Parkland uprising seemed to erupt out of nowhere, but it had been two decades in the making. The school-shooter era began at 11:19 A.M. M.D.T., on April 20, 1999. I arrived at Columbine High School, in Littleton, Colorado, a little after noon that day to cover the aftermath. The pain I witnessed is seared into me, but nothing prepared me for the next morning, when I saw the faces of the kids who had survived. Their eyes were dry, their faces slack. Their expressions had gone vacant. That’s why I’m still on the story two decades later. I never wanted to see that look again, but what we see today is worse: unsurprised survivors, kids who expected something like this.

The media coverage of Columbine was unprecedented. CNN logged its highest ratings ever, and The New York Times covered the story on its front page for 11 straight days. It was an exceptional moment, demanding exceptional action. Law enforcement and the education system responded with some important changes, including the “active shooter protocol,” and then . . . we came to accept it.

There were no vacant stares from the Parkland survivors. This generation grew up on lockdown drills, and they were primed for action this time. Jackie Corin and her friend Cameron Kasky crouched in lockdown for three and a half hours, getting updates on the carnage by text and Twitter, as 17 students and staff were killed around them—long enough to ride the waves of fear to simmering anger. Jackie and Cameron went to bed that night nursing notions that would give birth to a movement.

Speed. That was the first answer to the question on everyone’s lips this spring: Why is this time so different? Jackie, Cameron, and David Hogg started simultaneously, in the hours after the attack, on three separate and distinct paths. That was Wednesday, February 14. By Saturday, they had joined forces with Emma González and other emerging leaders to launch the #NeverAgainMSD movement.

Their efforts have upended the gun-control conversation in the United States, giving two decades’ worth of survivors new hope. “I am in awe of what is happening,” Coni Sanders told me in March. Her father, Dave, was the Columbine teacher who had remained in the building, saving hundreds of students, until he came face-to-face with the killers. He was shot and, hours later, died of his wounds. “It’s working,” Coni told me. “All these years and it’s working.”

It was speed, then it was candor. Shortly after dawn on the morning after the attack, David Hogg was on CNN, calling out adults for failing his classmates. “We’re children. You guys are the adults,” he said. “You need to take some action and play a role. Work together, come over your politics, and get something done.”

But as he spoke those words, David seemed to grasp that the kids would have to do it themselves. That Saturday, Emma rejected a lifetime of assurances that nothing could be done to protect kids from guns. “We call BS!” she declared six times in a searing speech that turned her into a national sensation by nightfall.

Speed and candor were critical to their launch, but the third element was vital to the goal of building an enduring grass-roots movement: the long, steady slog of igniting a youth-activist network across all 50 states.

At 17, Jackie can’t vote. She can’t even check into a hotel room, but that hasn’t stopped her from crisscrossing the country since Valentine’s Day, meeting with school groups and legislators. She estimates she has logged at least 30,000 miles, traveling as far as Kenya.

“I want to address the young people in the room that might not feel like they can do anything,” she said at a town hall in Denver. “I’m only 17. I’m not even old enough to vote. I am pre-registered. What you can do is, you can start clubs in your schools, you can join local clubs like Never Again Colorado, like Students Demand Action. You can talk to people that might not look like you, that might not understand your perspective on these issues. You can grab a clipboard and go to your local park and pre-register voters. You can do so many things, even if you can’t vote yourself.”

In fairness, Jackie has always been an over-achiever. Until high school, she was serious about dance. She did tap, jazz, and hip-hop, but her passion was pointe. “Dance was my life and my love,” she said. But she gave it up in high school, to focus on her studies and student government. As a junior, she took on five A.P. courses, though valedictorian was out. “Sophomore year I got one B-plus,” she told me. “It was my one B-plus my entire life.” She wasn’t going to let that happen again.

Her dad, Paul, describes her as brilliant and very emotional—“but she’s not showing it, because she’s laser-focused right now.”

I’ve never seen Jackie lose her composure, but she keeps telling me about breakdowns. An early one came about a week after Tallahassee, when she returned to Douglas High for the first time since the massacre. As she was leaving, a car ran over a water bottle. The pop sounded nothing like a gunshot, but triggers are often irrational. She sobbed uncontrollably for several minutes.

For weeks afterward, Jackie was terrified by bathroom trips. “The people who went to the bathroom in the freshman building—they were targets, because they were in the hallway,” she said. “They were easy targets. That’s what’s scary about it.” Out in the open. Unprotected.

Jackie’s fears have since faded, but they lurk and swell unpredictably, in waves of silent terror that can knock her back at any moment. Her adversaries do what they can to make it worse. Her team has been hounded by death threats and scary packages. The Parkland activists seem so confident and media savvy on television, but they are high-school kids. Most had never seen a gun until a SWAT team burst in and marched them out of their classrooms, hands raised.

Stealth fear was a constant companion on the #RoadToChange, this summer’s marathon bus tour across 15,000 miles of America. The tour was the movement’s big push to influence the midterms—which has been their objective ever since they concluded, way back on Valentine’s Day, that passing effective gun legislation meant changing our legislators.

“We could very well die trying to do this,” Emma González told me in D.C., a few hours before she closed the Washington rally with a speech climaxing in a spellbinding four and a half minutes of silence. “We could get shot by someone who’s like, ‘Don’t take away my guns.’ Which is not what we’re trying to do. We’re not trying to take away anybody’s guns. But they misconstrue our message, because they’re afraid of this becoming a slippery slope, or they’re afraid of us, because we have a voice now.”

The day after the shooting, Cameron Kasky began envisioning the big march. Five weeks to pull it off felt borderline reckless, but by the time he invited Jackie to join him the next day, she was already organizing another operation, with a fiercer sense of urgency: one week.

It started with a Facebook post.

Jackie posted it before going to bed the night of the shooting. That day, she had walked out of the freshman building 10 to 15 minutes before the gunman entered through the same doors. Jackie had organized a fund-raiser to sell Valentine’s Day carnations, and delivered them during her free hour. When the fire alarm sounded, she was back in study hall with her adviser, along with some autistic students. They hurried out to the bus loop, and a friend said she’d heard a gunshot. “No, you didn’t,” Jackie told her.

But people started running and yelling about a shooter. “I was really confused,” she told me later.

They had been trained to shelter in their classrooms, so they ran, suddenly frantic. “I had no idea who was behind me,” she said. “It could have been a whole team of shooters.” Or no one. She whipsawed between panic and eye rolling. “I was in denial like the first 15 minutes,” Jackie said.

She had reason to be skeptical. Her mother teaches at a nearby elementary school, and she wasn’t on lockdown. “I was texting her, and she was like, ‘Relax, Jackie. This is not real. We’re not on lockdown. We would have been on lockdown by now.’ ”

Suddenly, Mary Corin’s texts changed: “This is real. Active shooter. Just listen to your teacher.”

Jackie hunkered down in her classroom for three and a half hours. She heard a helicopter thuck-thuck-thuck outside her window as she watched its footage of her building on her phone. Cameron Kasky was there, too. When the SWAT team came, they burst in violently, shattering the glass in the door. Five hulking men barked orders and pointed assault weapons: “Hands up!”

It was terrifying, Jackie said, but she was most afraid for the autistic kids. “They were making noises, and some of them didn’t know to put their hands up when they were told to,” she said. “If they had made a wrong move . . . who knows?”

Jackie and Cameron staggered home shaken. And angry.

Classmates took to social media, pouring out their ordeals. Jackie wasn’t sure what to write. She was focused on her friend Jaime Guttenberg, who was “missing,” that ghastly euphemism for probably dead. She pounded out a Facebook post that said, “Please pray for my school,” worked up to a call for stricter gun laws, and ended, “MAKE IT STOP.”

“The end of my little message was that we need to make a change,” she told me. “I obviously didn’t know how. I had no idea.”

The next morning, she got word that Jaime was dead.

Local officials put Jackie in touch with her state senator, Lauren Book, who helped her shape and mobilize her plan: the lightning strike on the Florida State Capitol, in Tallahassee, just five days later. It should have taken a week or two to plan, but the legislative window was closing fast.

Senator Book spent Saturday and Sunday cajoling her colleagues. As the yeses multiplied, so did the logistics. Jackie sorted volunteer students into 10 rotating groups, to meet officials in intimate sessions. Senator Book compiled a profile on each official, which Jackie matched to students based on interests and personalities—“strong students with hardheaded legislators,” she said. Allied legislators created a crash course on lobbying for their late-night arrivals. UberEats and individuals donated the meals. Florida State University provided two sprawling rooms to accommodate cots donated by the Red Cross. Book insisted on paying the biggest expense—nearly $12,000 for the three buses—out of her own pocket.

Many parents were reluctant to support it. Much of Jackie’s weekend was consumed allaying their fears by cell phone.

Tuesday afternoon, six days after the attack, three jumbo buses loaded with Douglas High survivors snaked up the Florida Turnpike. The eight-hour trek was live-streamed by embedded journalists from CNN and other outlets. The kids met with 58 state officials that day, including every member of the Republican leadership: Senate president, House speaker, attorney general, and governor.

Two weeks later, Governor Rick Scott defied the N.R.A. and signed a modest gun-control bill into law. It banned bump stocks, raised the minimum age for buying a gun to 21, and added a three-day waiting period. (It did not address assault weapons.)

No one had seen that coming. After decades of defeats, the momentum of the gun debate had suddenly flipped. Jackie Corin gave her movement something it desperately needed. She gave it a win.

Cameron Kasky first tweeted #NeverAgain two days after the shooting. Wasn’t “never again” a Holocaust phrase?, his friends asked. Yes, but so what? They brushed it off and went with #Never-AgainMSD.

But they quietly inched away from it in the days leading up to the march. “We can’t actually use that, because it’s owned by the Anti-Defamation League,” said MFOL chief strategist Matt Deitsch. March for Our Lives became the official name.

MFOL was born in Cameron’s living room, and solidified that first weekend. The group initially comprised about two dozen Douglas students and five recent graduates—mostly Cameron’s friends from Drama Club, plus a handful from the school news channel and two others. Jackie was one of the two: an implementer among the creatives. They would add about 10 Douglas classmates in June, followed by more students from around the country during the summer bus tour.

They made two crucial decisions immediately: speak with one voice, and hammer one topic—guns. Over these first two decades of the school-shooter era, three major strategies have emerged to end it: addressing mental-health issues, eliminating easy access to guns, and ending media lionization of the killers. All three are daunting, but adversaries have stalled progress on each one by deflecting to the other two.

The Parkland kids seem to have accidentally solved the problem of celebrity shooters simply by becoming bigger celebrities themselves. It took David Hogg 24 hours to become the first survivor of a school shooting to surpass his attacker in fame. Emma González went viral shortly thereafter. Meanwhile, the gunman’s name has already been forgotten, and few people could pick him out of a lineup.

He is irrelevant, but his mental-health problems may not be. In August, police released a partial transcript of an interview conducted within hours of the attack, in which the killer insisted that a “demon” voice in his head had repeatedly cajoled him to commit violence. “Burn. Kill. Destroy,” the voice said.

The Parkland kids believe mental health is an important cause, but it’s not their cause. From the start, they saw one road to victory: throw all their weight behind the problem of guns.

According to the University of Washington’s Institute for Health Metrics and Evaluation, the U.S. averaged 3.85 gun deaths per 100,000 inhabitants in 2016, which is eight times Canada’s rate and 27 times Denmark’s. At least 138 people have died in American school shootings since the Sandy Hook massacre, in December 2012, as reported by the nonprofit Gun Violence Archive. Earlier this year, Russia was alarmed by a string of school stabbings, with some of the assailants citing Columbine as their inspiration. But nobody died. The difference: guns are very difficult to obtain legally there.

The Parkland kids decided their demands must be extensive and specific, yet reasonable. Above all, they pledged to keep their hands off the Second Amendment. They didn’t want to cause trouble for hunters, gun collectors, or gun enthusiasts—but they didn’t think hunters had the right to a Howitzer or an M16. So they all dived into research: What had been tried already? What worked, what failed, and what did the American people support? What did gun owners themselves support?

The N.R.A. closely guards its membership data but claims nearly five million members—“and David Hogg is three of them,” Jackie told a town hall in Denver. “Lots of people like to buy us memberships.” She always gets a laugh with that line. Even if the five million figure is accurate, it represents just 1.5 percent of the population. Yet the N.R.A.’s aura of invincibility goes largely untested, because politicians so rarely risk opposing it, even on trivial matters. Every “wrong” vote, even for legislation backed by 90 percent of constituents and solid majorities of gun owners, chips away at a legislator’s N.R.A. score and can energize a primary opponent.

That’s why it was so important to notch an early win. “You have to begin to slowly build momentum, because most voters don’t have a lot of faith in anyone out-maneuvering the N.R.A.,” said John Della Volpe, director of polling at the Harvard Kennedy School Institute of Politics. “You need to believe there’s an opportunity that you can win. It gives voters, especially young voters, faith. And the Parkland students, they’ve had more success already than many others have in many years. I believe that has to be part of their narrative. ‘We’ve done this, we’ve done that: help us take it to the next level.’ ”

Della Volpe told me that in June. Jackie Corin had come to the same conclusion by day two. “If we were all talk and no action, people wouldn’t take us as seriously,” Jackie said. “We needed a critical-mass event.”

Della Volpe was impressed by how these kids understood they had launched a generational campaign. Even if they devote their lives to the fight, they will likely hand the baton to kids who have not yet been born, he said.

“Just like the civil-rights movement took years, this is going to take years,” Jackie told me.

The Columbine generation has been practicing lockdown drills since kindergarten, watching one suburban school after another attacked, wondering if they were about to lose the lottery. Year after year brought a fresh crop of devastated kids—most of them affluent, telegenic, and white. Meanwhile, students in inner cities were far more likely to die from gunfire than their suburban counterparts. In the month of the Parkland shooting, according to the Gun Violence Archive, there were 84 teen deaths in America, 5 in Chicago alone. And through mid-August of this year, 1,846 have been killed or injured, many in the inner cities. Their stories rarely made the evening news.

It bothered the Parkland kids that a far larger cohort of kids, facing far worse odds, were being ignored. So they decided to join forces with them.

Chicago is ground zero in the urban gun wars. In early March, a small group of student activists flew from Chicago to meet the MFOL kids at Emma González’s house. “When I first got there, it was a gated community and I thought it was a hotel resort or something,” Alex King said. “And then I saw the house. There was like this big glass window that was also a door, and I was like, ‘Wow, O.K.’ When I actually got in there, Emma came around the corner running, hugging everyone—it was just like happy faces all around the room.”

As the groups got to know each other, they learned that their fears were different. Suburban kids tend to fear gunmen bursting into their schools; urban kids fear gunfire en route. Swapping gun stories got pretty intense, and during a break Emma chatted with D’Angelo McDade about turning suffering into action. That reminded him of something. D’Angelo and Alex were representing the Peace Warriors, an “interrupter” group that seeks to resolve neighborhood conflicts before they turn violent. D’Angelo reached into his pocket and drew out six colored dog tags. The red one said PRINCIPLE #4, with a peace sign—that was it. Martin Luther King Jr. preached six principles of nonviolence, D’Angelo explained. The Parkland kids were embarking on No. 4: SUFFERING CAN EDUCATE AND TRANSFORM. And King singled out a particular kind of suffering: “Unearned suffering is redemptive and has tremendous educational and transforming possibilities.” Sound familiar?

“Oh, wow, can we do this all together?” Emma asked.

The full group reconvened. “We taught them the principles, and they taught us about policy,” D’Angelo said.

The principle that most influenced MFOL was No. 3: NONVIOLENCE SEEKS TO DEFEAT INJUSTICE, NOT PEOPLE. Gun violence is the enemy, legislators’ blocking solutions were a problem, and those legislators were adversaries, not enemies—and that was a gaping difference, not a grammatical point. Even if they had been corrupted by N.R.A. money, none of those people were evil, and none of them deserved to be treated as if they were.

MFOL was still developing its agenda for change, and the meeting helped shape it. Instead of talking about “school shootings,” they would address “gun violence.” The media barely noticed the distinction, but it was crucial to the kids.

In March, they announced their five demands: (1) universal, comprehensive background checks; (2) a digitized, searchable database for the Bureau of Alcohol, Tobacco, Firearms and Explosives; (3) funding for the Centers for Disease Control and Prevention to research gun violence; (4) a ban on high-capacity magazines; (5) a ban on semi-automatic assault rifles. None of them was specific to mass shooters or schools. If people thought of them as pertaining only to kids, that was fine—as long as it was kids of all backgrounds.

The MFOL and Chicago kids would meet several more times over the spring, culminating in the Peace March on the South Side of Chicago, which would kick off the #RoadToChange summer tour in June. Nearly a dozen of the Chicago activists would hop on board for the first week or two of the tour, and three stayed for the entire tour.

The MFOL team has been crisscrossing the country since Valentine’s Day, attending high-school and college events. All that local contact crystallized their phase-two strategy long before the march: Leverage the enthusiasm. Organize it.

Early on, they noticed something significant: Every high-school visit required a student to invite them, win faculty approval, and recruit classmates to execute the event. The simple act of visiting these schools was activating young leaders and giving them a taste of organizing. MFOL couldn’t hit 435 House districts. It could not hit thousands more state and local electoral regions. The kids they connected with could.

Every event, no matter how big or small, modest or glamorous, came with one demand: voter registration—a table or booth or preferably a clipboard team hitting up the venue and the parking lot. David Hogg was frequently seen working the crowd. Their mantra was simple: “You can’t vote if you don’t register.”

Young voters have long been a sleeping giant of American politics, because most of them stay home. If they ever turned out in percentages to match their older counterparts, they could swing many elections. Trouble is, they never have.

Over the past year, however, young people have been turning out to vote in special elections. Harvard’s Della Volpe, who has been studying young voters for two decades, says there are signs that this year really could be different. “Young Americans vote when they believe their efforts have tangible results,” he says, and his research shows that they are now 50 percent more likely to say politics matters than they were pre-Trump. Democrats are particularly charged up. In spring 2018, Della Volpe found that the number of registered Democrats between the ages of 18 and 29 who said they intended to vote surged to 51 percent, from just 28 percent in 2014. On the Republican side, the number rose from 31 to 36 percent.

What’s more, there are signs that gun control is finally becoming a viable issue on the left. The established wisdom has always been that Democrats don’t vote on guns. Neither do most Republicans, but a small subset does—sometimes enough to sway a primary. This asymmetry allows a tiny minority to consistently defeat huge majorities, or to convince politicians they will.

A media analysis published by the Trace, a nonprofit news organization that tracks gun issues, found that, in the three and a half months after Parkland, the number of news stories mentioning guns was more than double the number that appeared following any of the seven worst mass shootings since 2013. And the increased coverage continued for six weeks, versus two to three weeks for the others.

In late spring and early summer of this year, some national polls showed that gun policy had zoomed up to third or fourth place among priorities for voters heading into the midterms—after the economy and health care, but ahead of immigration and taxes.

The morning of the March for Our Lives, early arrivals in Washington were enthusiastic but jittery. The kids had hoped to inspire dozens of sibling marches, perhaps even a hundred or two, but the number had ballooned to 800. Some true believers I spoke to that morning feared that was a strategic mistake. As the crowd formed, one person after another told me most of their friends had stayed home to attend local marches. Would that drain their force? All the coverage would hinge on the number of people who turned out in Washington. No one would remember how many people showed up in Denver.

Denver noticed. The nation’s 19th-largest city drew more than 100,000 people, according to Denver’s Westword weekly. Colorado was stunned. Organizers were stunned. “On Facebook it was about 30,000 who said they were coming . . . and it jumped so fast!” said Jessica Maher, one of the Denver organizers. Jessica was a college senior who had never done anything politically active in her life. Now she is the director of political affairs for Never Again Colorado. The waves of supporters pouring into Civic Center Park and marching around downtown Denver on March 24 changed everything. This was real, she realized. This was powerful.

The true main events that day, 800 sibling marches around the world, were largely reported as an afterthought. They were organized by high-school kids and college students, many of them political neophytes who had never even voted. A massive national organization was creating itself in the image of the template forged in Parkland. MFOL affiliates now number over a thousand, Jackie said.

“They tend to, like, fangirl—and I wish they didn’t, because we’re just normal kids, but it’s nice for us to give that to them,” Jackie said. “They’ve been looking at what we’ve been doing, and they were inspired by us to create something at their school and in their town.”

The summer demanded something big. MFOL could never top the D.C. march for national exposure, but they were focused on local networks now. The kids could see the impact they’d been having, energizing schools all spring, usually traveling in small groups of two or three. What if they multiplied that?

They brainstormed for weeks and came up with the #RoadToChange bus tour. It was actually two tours, one across America and the other across Florida, hitting every congressional district in their home state. MFOL prides itself on being nimble, and midsummer the Florida tour was re-christened the “Southern Tour” and expanded to include Alabama, Mississippi, and Louisiana. Combined, the roughly three dozen members covered more than 15,000 miles from June to August, visiting 50 cities in 28 states and speaking to 50,000 people.

They knew they had to go to gun country. “Most of the tour stops are the places where it’s most likely people disagree with us,” Jackie said—the Farm Belt, the Mountain West, and the Deep South. “We want them to show up and listen to what we have to say. They’ll bring back that conversation to other people that disagree.”

Town halls were the tour staple. They typically wrapped around nine P.M., followed by selfies, one-on-one connections with audience members, and dinners with local organizers. It was usually midnight by the time the kids staggered back to their hotel rooms. Then they’d wake up around dawn, drive four to eight hours, and repeat. Halfway through, in Denver, the Parkland kids were still in good spirits, but many confided that the grueling schedule was wearing them down.

“You eat unhealthy food and you don’t sleep properly and your body’s just always confused,” Jackie said. But her big challenge was the logistics. She had taken the lead on organizing all the events.

Whatever cornfields or mountains were rolling by her bus window, Jackie’s head and phone were several days and thousands of miles ahead, arranging venues, permits, publicity, and speakers. She coordinated with local chapters to handle a thousand tiny details, like T-shirt sales and check-in wristbands, and of course all those kids with clipboards registering young new voters.

“Every morning I wake up to anywhere between 20 and 100 texts,” Jackie told me in late July, as she geared up for the tour’s final leg. She typically works with three to four lead organizers in each city, and is juggling several states at a time.

Each event is an undertaking, forcing newly formed local groups to work together. The key is building connections. “Teenagers are sometimes nervous to make friends and stuff,” Jackie said. “So creating a network of kids and organizations that can help each other without us being the mediators is so important. Because we’re not superheroes.”

The MFOL team scours each city for promising young leaders. Every few stops, they coax one or more on board. They arrived in Denver with four kids they had picked up in Houston, one from Milwaukee, and three from Chicago, plus one from Harlem they had connected with earlier. They give them crash courses in public speaking and other skills. For the first time, MFOL expanded beyond Douglas students and recent graduates on the bus tour, widening out to a national network, with many of these new recruits full members of the national team.

At times, the tour got tense. Pro-gun groups followed the bus for four straight days across Texas and the one day in Utah. Some of the kids were shaken up, especially the ones struggling with PTSD. “People had like two A.R.’s, two pistols, two handguns strapped on their belt, and a knife,” Jackie said. “Are you trying to prove a point? Because you look dumb.” She was a bit rattled, but not deterred.

The Utah group got some free publicity by frightening MFOL’s Salt Lake City venue into canceling. “We are getting a new venue! No worries!” Jackie tweeted that evening. She had three days to do it as they pulled into Denver. “A lot of venues reached out to us in the area because they felt bad,” she told me. “The other venue just canceled because they were scared for security reasons, because we are security targets. We’re targets.”

Before February 14, Jackie’s plan was to graduate in the top 1 percent of her class and then pursue a nursing career. “I was on the road to getting straight A’s this year, and I was going to, but I was on a trip for the Time 100 gala, and I couldn’t take my math final,” she said. For the first time, Jackie had to choose between academics and activism.

Even after she skipped the final, her pre-calc scores were high enough to give her a B-plus. “I was top 1 percent of my class, but now I’ll be like top 15 percent. That’s fine,” she said. “It messed up everyone. Everyone in the group is smart, and all of our G.P.A.’s dropped, because we just didn’t have time.”

Jackie had four A.P. classes scheduled for senior year, but pared it back to just one. “I didn’t feel the need or want to force interest in pre-calculus,” she said. “I’ll look at the board in my English classroom and be like, ‘This isn’t helping me.’ ”

Jackie hated that sort of talk “before it,” as Parkland students refer to life pre-attack. She kept one A.P. course—A.P. Government—“because it’s probably what’s going to intrigue me,” she said.

Late in February, weeks before the D.C. march, she told me she was starting to consider a career in politics—a prospect she found startling but also electrifying. “Older people—they’re listening to me,” she said. “I didn’t know I had this powerful voice that I could use for good.”

Then she spent months mucking around with politicians. She was not impressed. “I don’t really know what I want to do, but I feel like I don’t want to be a politician when I’m older,” she told me in June. “Politics is always going to be dirty. And I don’t want to be around that environment.”

She envisions a nonprofit role helping improve kids’ lives. She plans to keep up the gun fight for a while, but not forever. “I feel like I work well with kids,” she said. “I quit my camp-counselor job this summer to do #RoadToChange, but it breaks my heart because I’m not with my girls.”

One thing is certain: she’s given up rushing to nail her future down. “I’m learning so much this summer by just being present in these places,” she said. “Before all this, I was always the person who had my future set and planned. And now there’s nothing about my life that’s set and planned. So it’s a very different way of living, but the discomfort is kind of . . .” She trailed off. “I don’t know the word for it. I’ve been getting adjusted to the discomfort, actually—that’s a better way to put it. Because before I was always comfortable, and this discomfort is new, yet welcoming.”

When the movement was just beginning and its future uncharted, Jackie foresaw a generational struggle. Four months later, with thousands of miles in the rearview, I asked her if that vision had changed. “I was just kind of thinking of all the movements that initiated change before,” she said. “It truly was generational. Though election cycles can change things, it’ll take a generation of people to understand that they don’t need these weapons.” She has met a lot of people in gun country this year, and heard a lot of them say, “I’m a responsible gun owner; I didn’t do anything wrong.” She understands that. But her generation, trained to expect a gunman to burst into their classroom any day, tends to see it differently.

Her goal is not a decisive win this November and sweeping gun reform this spring. It’s passing one reasonable law after another to reduce gun violence without cramping the style of responsible young gun owners. “When they have kids, when they grow up with this all the time and they’ve seen the positives that these laws will create from a young age, they will understand,” she says. “It’ll take a generation. And it’s unfortunate, but I just hope that when we have children, they will probably, hopefully, end up in a society where these laws are implemented and understand the importance of them.”

When Jackie, Emma, David, and the others hand the reins to the next generation, they want their movement to be more powerful than the N.R.A. That will mean many rounds of big wins, and inevitably some setbacks. The first real test comes November 6. TargetSmart, a data firm which works on behalf of Democrats, released an analysis in mid-July showing big increases in youth-voter registration in key battleground states across the country since Parkland. In Florida, it surged 41 percent in the two and a half months after the shooting.

Now MFOL has to get those waves of new voters to the polls. They’ve got a thousand new affiliates in the field, and the big task for the fall is building out a stronger infrastructure, “so a random kid from Texas could talk to someone in Idaho and connect and organize together,” Jackie said.

When the bus tour pulled into its final stop in Newtown, Connecticut, on August 12, they had 12 weeks to tighten up their organization for Election Day, and two years to prepare for 2020. Three days later, Jackie was back in Parkland for the first day of senior year. The next week, I asked how it felt to be back in school. “Oh, God,” she groaned. “It kind of feels like an extracurricular.”

Jackie had apologetically rescheduled our phone conversation three times as she juggled calls with local affiliates. We finished two minutes ahead of her nine P.M. call with Seattle. Before all this, her bedtime used to be eight o’clock.

Of the thousands of young activists Jackie has befriended since February, one stands out. She met Natalie Barden at the Teen Voguesummit in June. Natalie was in fifth grade when she lost her little brother, Daniel, at Sandy Hook. For five years, Natalie avoided the gun conversation—it was just too painful to talk about. Parkland changed everything. She went to the March on Washington, “and was moved beyond belief,” she wrote.

“When she saw us do it, she felt empowered,” Jackie told me. “Because when her little brother died she was 10.” Natalie was Jackie’s lead organizer in Newtown, helping her plan the four-hour rally with food trucks, entertainment, speakers, and a meeting of MFOL kids and Sandy Hook survivors. “She did an amazing job,” Jackie said. “When you have a connection to the issue, it doesn’t even feel like a job.”

Jackie feels like she’s passing the torch, but she’s really lighting activist flames across the nation. “March for Our Lives does not belong to us anymore,” Jackie said. It belongs to every kid in America who is ready to heed the call.