In describing his departure from one of his baseball managerial posts, Casey Stengel once said, “We call it discharged, because there is no question I had to leave.” So it may be with the Deputy Attorney General of the United States, Rod Rosenstein, who, the White House announced on Monday, will meet with Donald Trump on Thursday. There are questions about whether Rosenstein has offered his resignation, or intends to be fired, but it is now likely that Trump will get what he has long wanted—Rosenstein’s exit from office. Rosenstein appointed Robert Mueller as the special counsel and, more to the point, protected his investigation from Trump’s all-but-explicit demands that he dismiss Mueller. Now, if Rosenstein is gone, who, if anyone, will make sure that Mueller’s work can continue?

This is at once a narrow jurisdictional question and a major political issue. The narrow matter relates to the official hierarchy of the Department of Justice. After Jeff Sessions, the Attorney General, recused himself from the Russia investigation, the responsibility for the issue fell to his deputy, Rosenstein. So, if Rosenstein is out, the matter would ordinarily fall to the department’s No. 3, the Associate Attorney General, but that post is vacant, meaning that it would go to the Solicitor General, Noel Francisco, who ranks fourth. But the matter may be more complicated. According to Marty Lederman, a professor at the Georgetown University Law Center and a former Justice Department official, Francisco might also have to recuse himself, because his former law firm, Jones Day, still represents the Trump campaign. That would leave supervision to Steven Engel, the Assistant Attorney General for the Office of Legal Counsel—at least until Trump fills the post of Deputy Attorney General. Complicating matters further, as Lederman notes, and as Ian Millhiser, of the Center for American Progress, has pointed out, it’s not clear if Trump can fill that post unilaterally—that is, without the advice and consent of the Senate.

This issue of who, technically, would be in charge of Mueller is an important one, but it’s not nearly as significant as the broader issue raised by Rosenstein’s likely departure. The President is in charge of the executive branch, and Mueller, as the special counsel, is a subordinate in that branch of the government. If Trump is determined to fire Mueller, or to constrict his investigation in untoward ways, he and his advisers will figure out a way to do it. There is little doubt that the President could ultimately find a compliant Justice Department official to carry out his order of execution. In other words, the massacre this week may lead to another, like the one on a Saturday night in 1973 when Richard Nixon fired Archibald Cox, the Watergate special prosecutor. This modern version would be an abuse of power of the most profound sort. Firing Mueller—who has been investigating Trump and his campaign and Administration for a year and a half—would be the very definition of a high crime and misdemeanor, as impeachable offenses are defined in the Constitution. But would the Republicans who control Congress see it that way?

Put another way, the real question is whether there is any political will among the Republicans who run the legislative branch of government to check Trump’s power. One of the signal features of the Trump Presidency has been the abject surrender of the Republican Party, especially in Congress, to all of Trump’s demands. Most congressional Republicans have made dutiful statements urging the President not to fire Mueller, but will they really take any action if Trump actually does it? Their history suggests that they will not—and they may soon have the chance to test that hypothesis. Mueller’s fate has never looked more precarious than it does today, and he would be foolish to think that the Republicans in Congress would do anything to protect him.