The good news is that no one, including Mr. Whitaker, can stop the multiple prosecutions or litigation already in progress — including the cooperation of Paul Manafort; the sentencing of Michael Flynn; or the continuing investigation of Michael Cohen, Mr. Trump's former lawyer, and the Trump Organization by federal prosecutors in New York. The courts will have the final say on what happens in each of those cases.

Democrats will also soon be running the House, returning it to its place as a coequal branch of government and holding Mr. Trump to account for the first time since he took office. “We are immediately issuing multiple letters to key officials demanding that they preserve all relevant documents related to this action to make sure that the investigation and any evidence remains safe from improper interference or destruction,” Representative Jerrold Nadler, the New York Democrat who is expected to soon head the House Judiciary Committee, said in a statement on Wednesday.

The bad news is, well, pretty much everything else. Mr. Whitaker — who has been called the “eyes and ears” of the White House inside the Justice Department by John Kelly, Mr. Trump’s chief of staff — has expressed a Trumpian degree of hostility to the investigation he is now charged with overseeing. He has called it a “witch hunt” and, in its earliest months, wrote an opinion piece arguing that Mr. Mueller was coming “dangerously close” to crossing a “red line” by investigating the president’s finances. He has suggested there was nothing wrong in Mr. Trump’s 2017 firing of James Comey, the F.B.I. director, and he has supported the prosecution of Hillary Clinton. In an interview last year he described “a scenario where Jeff Sessions is replaced with a recess appointment, and that attorney general doesn’t fire Bob Mueller, but he just reduces his budget to so low that his investigation grinds to almost a halt.” In 2014, he headed the political campaign for Iowa state treasurer of Sam Clovis, who later became a Trump campaign aide and, more recently, a witness in the Russia investigation.

Conflicts of interest like this are what led Mr. Sessions to recuse himself from the Russia investigation. That was the ethical thing to do, even if it sent Mr. Trump into a spiral of rage.

Mr. Sessions, a veteran of the Senate, is an institutionalist at heart. “The Department of Justice,” he once said, “will not be improperly influenced by political considerations.” That sentiment was never going to survive long under Mr. Trump, for whom improper influence has been a central plank of governing philosophy. Ethics, not so much.