Second, the investigation has already progressed very far. It is one thing to squelch an investigation in its crib. It’s another thing to squelch an investigation that has already collected important evidence and brought key cases. The effort to do so cannot take place invisibly, as a great many prosecutors and FBI agents will be aware of what is happening. None of them has to leak anything for that awareness to find its way to Capitol Hill, because the Hill is already aware of the problem and looking for signs. Mueller is by many accounts writing a report, a step that signals a completed investigation or a completed portion of an investigation. The effort to suppress that report could be politically galvanizing and, in its own way, as damaging for the administration as the contents of that report when they eventually become public.

Third, Mueller does not have to remain silent. Mueller has used silence as a powerful strategic instrument throughout his investigation. He has done this for a variety of reasons, and the silence has served him well. Among other things, it has given his voice, if and when he ever chooses to use it, enormous moral and political power. The day that Mueller holds a press conference or stands before cameras and declares that his investigation is facing interference from the Justice Department will be a very big day, perhaps a game-changing day. If the department suppresses his report, he has the capacity to, as James Comey did after his firing, testify before Congress about what happened. Mueller has not hoarded power or jurisdiction, but he has hoarded moral authority. If Whitaker or his successor seeks to frustrate the probe, Mueller can spend down those huge reserves of credibility.

Adam Serwer: Trump will only get more dangerous.

Fourth, the midterms matter—and they mean investigations. Squelching a high-profile, politically explosive investigation of the president is hard enough in this country under any circumstances. When the opposition party controls powerful congressional committees and is committed to oversight, it’s that much harder. The Democratic takeover of Congress means that key committees will be watching every move Whitaker and his successor make with respect to the investigation. It means subpoenas for any report they may try to suppress. It means an open and receptive forum for Mueller to testify should he have something to say. It means constant investigation. And it means that the threat of impeachment hangs over everything. This is a very big change, and Mueller is as aware of it as anyone. As a result of Democratic control of the House, he could, for example, write an unclassified summary of his report and conclusions with every expectation that major congressional committees would demand it and release it publicly. He could also, say, write an impeachment referral—if he thought he had evidence Congress needs to see—and dare Whitaker to prevent its transmission to Congress. If Whitaker were to do so, Mueller could resign and announce what happened and let Congress do the rest. Having Democrats in control of the House matters enormously.