With Steve Bannon escalating his campaign to overthrow the G.O.P. establishment, Republicans are reportedly growing worried that Donald Trump’s tacit support for his former chief strategist’s tactics could unwittingly hasten his own impeachment. “The No. 1 thing Trump should be doing to save his presidency is helping congressional Republicans maintain their majorities,” Alex Conant, a G.O.P. consultant, told CNN, voicing a concern that lawmakers reportedly whisper in private. “Instead he’s allowing his allies like Steve Bannon to really undermine Republican re-election campaigns. It’s just reckless and politically naive considering how devastating it would be to his presidency.”

It is not surprising that Trump has grown dissatisfied with his fellow Republicans. With few legislative accomplishments to his name, Trump has placed much of the blame on Senate Majority Leader Mitch McConnell, Speaker of the House Paul Ryan, and other rank-and-file Republicans who he believes botched the Obamacare repeal. And he has complained that he received poor advice when he sided with McConnell to back the losing candidate in last month’s Alabama Senate primary race, the incumbent Luther Strange over the Bannon-backed Roy Moore. “Alabama was a huge blow to his psyche,” one person close to Trump told my colleague Gabriel Sherman last week. “He saw the cult of personality was broken.” Those frustrations boiled over Monday during an impromptu press conference with McConnell in the Rose Garden. “There are some Republicans that should be ashamed of themselves,” Trump said. “So I can understand fully how Steve Bannon feels.”

Trump, who came to power as a populist insurgent himself, has always been more comfortable playing the anti-establishmentarian. But Republicans are concerned that Trump doesn’t seem to grasp the self-destructive nature of his rhetoric, according to a CNN report published Monday. “If we lose the House, he could get impeached. Do you think he understands that?” one top Republican donor reportedly recalled a G.O.P. senator wondering aloud. “Won’t it be ironic that Steve Bannon helped get the president elected and impeached?” another Republican official said, according to CNN.

The fear is that Bannon’s roster of populist congressional hopefuls will defeat incumbent and establishment candidates in the Republican primaries, only to lose to Democrats in the general. And while the G.O.P. is expected to maintain control of the Senate, a power shift in the lower chamber could stall the Republican agenda, usher in a wave of subpoenas and scrutiny for the White House, and—most notably—set off impeachment proceedings. “It will be on steroids, the amount of lawyers, investigations, inspector generals that come out of the woodwork,” if the Democrats win back the House, Sara Fagen, who served as George W. Bush’s White House political director, told CNN. “It will be very debilitating in a way they don’t understand yet.” Another G.O.P. strategist echoed the sentiment. “Once the House is lost, then it just becomes, ‘Let’s look into Don Jr.’s tweets, let’s subpoena his country club locker,’” they said, adding, “Nothing is going to get done.”

Trump may have already lost the Senate. Despite his awkward attempt to make nice with McConnell during their joint press conference Monday, the president remains at odds with Republican Senators John McCain, Susan Collins, and Lisa Murkowski, all of whom served as critical votes against Obamacare repeal, as well as moderates like Jeff Flake and former primary opponents like Marco Rubio. Those tensions broke into the open last week when Senator Bob Corker told The New York Times that the president’s erratic behavior could be a national security risk. Trump dismissed Corker as “a fool,” but privately, many Republicans were said to agree with his assessment. “He is a reasonably powerful member of Congress and he has the respect and affection of the rest of the Republican caucus,” Louis Michael Seidman, a constitutional law professor at Georgetown University, told me. “He is not someone like [Ted] Cruz or [Rand] Paul who people think less highly of . . . my understanding is that he has a lot of sway with his colleagues.” He is also one of several senators who could endanger Trump’s presidency should he decide not to defend him. “It is always a good idea not to piss off the chairs of important committees and certainly that all the more so when you anticipate needing something from them in the near future,” Josh Chafetz, a constitutional law professor at Cornell Law School, told me.

Marc Short, the White House director of legislative affairs, dismissed the idea that Trump is oblivious to the fresh hell he could face if Democrats won the House. “I think the president’s keenly aware of that,” he said. Short also pushed back on the belief that the G.O.P. is guaranteed to lose power in the lower chamber, telling CNN, “We don’t have a defeatist approach on this.” Democrats, for their part, have already tried to weaponize Trump’s remarks against him and the Republican Party. “For once, President Trump is absolutely right that Speaker Ryan and Congressional Republicans are not getting the job done for the American people,” a Democratic Congressional Campaign Committee spokesman said in an e-mail blast shortly after Trump and McConnell’s joint presser.

Of course, it’s also possible that Bannon’s war on the Republican establishment could—whether by chance or by design—ultimately save Trump from impeachment. As Sherman reported, the Breitbart News chief has made it known that he pegs Trump’s odds of lasting the entirety of his term at 30 percent. Impeaching Trump would require buy-in from two-thirds of the Senate, which would necessitate Republican support. By targeting McConnell allies, Never-Trumpers, and institutionalist lawmakers, Bannon could be pre-emptively purging Congress of Republicans who might vote to oust the president. “In any impeachment scenario, the Republican base is likely to be whipped up into a pro-Trump frenzy,” writes New York’s Jonathan Chait. “Which senators are most likely to stand up to the base? Probably the same ones who would oppose angry demands for McConnell’s head on a pike.” It’s a “crude but potentially effective heuristic for identifying secret enemies,” he notes, but also a risky strategy if Trump really were to face impeachment. Replacing McConnell loyalists with Bannon-approved street brawlers could ensure Trump survives a constitutional challenge. Waging war on the establishment and losing could cost Trump more than just his presidency.