As special counsel Robert Mueller’s investigation accelerates, President Donald Trump is beginning to talk openly about using his pardon power to undermine the F.B.I. probe into alleged campaign collusion with Russia. In a stunning admission of the legal jeopardy in which he finds himself, Trump on Saturday tweeted that he has “complete power to pardon,” confirming earlier reports that he has been exploring his options with his attorneys. According to The Washington Post, the president has told aides he is “especially disturbed” at the prospect of Mueller accessing his tax returns—a red line that Trump warned Mueller against crossing in an interview with The New York Times on Wednesday.

With his first public acknowledgment that he is considering using his pardon power, Trump has established several potential lines of defense against Mueller, all of which presage a potential constitutional crisis. In his interview with the Times, the president outlined a scenario in which he could order Deputy Attorney General Rod Rosenstein, who is overseeing the Russia investigation after Attorney General Jeff Sessions recused himself, to fire Mueller. The Times reports that the White House is racing to identify possible conflicts of interest within Mueller’s team to discredit him. On Friday, he moved his White House onto a war footing, hiring the pugilistic Anthony Scaramucci to take over his communications office, prompting press secretary Sean Spicer to abruptly resign. Now he is openly floating the possibility that if he cannot successfully dissuade or dislodge Mueller, or if his P.R. offensive fails, he may resort to more radical measures to protect his family, administration, associates, and potentially even himself, from prosecution.

The Post notes that no president in the history of the country has sought to pardon himself, so there’s no legal precedent for what might happen if Trump tried. The theory that a president could escape obstruction-of-justice charges by exercising his pardon power to obstruct justice has never been tested. When it was first reported that the president and his lawyers had been exploring his powers, those discussions were described as hypothetical. As of Saturday, Trump has officially established the prospect as a very real possibility.

If the constitutional ramifications of such a move are unknown, the political fallout would be clear. But Trump’s team, for now, appears to be circling the wagons regardless. “The fact is that the president is concerned about conflicts that exist within the special counsel’s office and any changes in the scope of the investigation,” one of Trump’s lawyers, Jay Sekulow, explained earlier this week. “The scope is going to have to stay within his mandate. If there’s drifting, we’re going to have to object.”