Even in this news-addled Trump era, Sunday afternoon usually marks a lull: a time for reporters and politicos to indulge their social-media habits by tweeting about football, or even, perish the thought, to spend some time with their families. Not this week. Just before 4:30 P.M. on Sunday, the political class was jerked back to attention when Nick Ayers, the youthful chief of staff to Vice-President Mike Pence, let it be known on Twitter that he had turned down the chance to replace John Kelly as the White House chief of staff. “Thank you @realDonaldTrump, @VP, and my great colleagues for the honor to serve our Nation at The White House,” Ayers wrote. “I will be departing at the end of the year but will work with the #MAGA team to advance the cause. #Georgia.”

Journalists weren’t the only ones surprised by the Ayers development. It took many people in the White House unawares, including the President, it seems. The Times’ Maggie Haberman reported that “two people close to Mr. Trump said a news release announcing Mr. Ayers’s appointment had been drafted, and that the president had wanted to announce it as soon as possible.” Instead of showcasing as his new majordomo a blond, thirty-six-year-old Republican operative who has spent the past two years helping keep Pence out of any serious scrapes—quite a feat in the Trump White House—Trump was forced to engage in some Sunday-evening damage control.

Shortly after dinner hour, Trump tweeted, “I am in the process of interviewing some really great people for the position of White House Chief of Staff. Fake News has been saying with certainty it was Nick Ayers, a spectacular person who will always be with our #MAGA agenda. I will be making a decision soon!” Other White House officials emphasized that Ayers has three young children, and said that he had decided to return to Georgia, where he is from, to spend more time with them. “Those of us with young kids very well understand the personal decision he made,” Kellyanne Conway told the Times.

To say that the inhabitants of the media-political bubble greeted this explanation with skepticism would be an understatement. Summing up the general reaction, John Podhoretz, the New York Post columnist and editor of Commentary, said on MSNBC, “That’s a lot of crap. I don’t know Nick Ayers. I’m not saying he’s a liar, but people don’t get offered the White House chief-of-staff job very often. He was the Vice-President’s chief of staff. This is the center of the action. This is the red-hot center of world politics and world power. And he is going back to Georgia after being the chief of staff to the less-important guy? I am not buying it.”

Neither am I, John. Regardless of Ayers’s personal situation, the takeaway here is that a savvy, ambitious young Republican—one with strong links to the donor class that plays such a key role in the Party—has spurned the President. This just two days after federal prosecutors from the Southern District of New York said that Trump had directed Michael Cohen, his former fixer and personal lawyer, to carry out two campaign-finance felonies, and the special counsel, Robert Mueller, said that Cohen had provided his team with“useful information concerning certain discrete Russia-related matters core to its investigation.”

As Ayers’s tweet indicated, he isn’t abandoning Trump completely. The White House let it be known that he plans to head up a pro-Trump super PAC for the 2020 campaign. Right now, though, 2020 is an eternity away. With the Democrats about to take control of the House of Representatives and the Mueller investigation seemingly reaching a climax, Trump needs all the help that he can get immediately, including a politically savvy chief of staff. Ayers declined to fulfill that role.

In a party in which allegiance to Trump among many elected officials has long been based on fear and self-interest rather than any genuine liking, this decision sends an alarming signal to Trump and his allies. After all, Ayers wasn’t in any sense an outsider. According to all reports, he had a good relationship with Trump, and with Jared Kushner and Ivanka Trump, who supported his promotion to Kelly’s job. If a figure this connected has decided to hop off the Trump train—or at least to move to a carriage farther back—how long will it be before other Republicans follow his lead?

Steve Bannon is warning that it might not take long at all. Over the weekend, the former Trump strategist told the Washington Post that 2019 would be a year of “siege warfare” for the White House, and he went on, “The president can’t trust the GOP to be there when it counts. . . . They don’t feel any sense of duty or responsibility to stand with Trump.”

Bannon isn’t a wholly reliable observer, of course. But, in this instance, what he said may well be true. Trump didn’t win over the Republican Party: he conquered it. And, over the weekend, in the wake of Mueller Friday, there was a notable shortage of senior Republicans coming to the President’s defense.

The task was largely left to Senator Rand Paul, a longtime critic of the Russia probe, and Chris Christie, an ally of the President. And even Christie, who has been mentioned as a possible candidate for the White House chief-of-staff job, wasn’t all that reassuring. Appearing on “ABC News This Week,” the former New Jersey governor, who also served for eight years as a federal prosecutor, conceded that if he were one of the President’s lawyers he would be concerned about the Southern District’s sentencing memorandum. “The language sounds very definite, and what I’d be concerned about is, what corroboration do they have?” he said.

Trump’s enduring strength, of course, is his support at the base of the G.O.P. In the latest NPR/PBS NewsHour/Marist College Poll, which was carried out last week, before the release of the sentencing memos for Cohen and Paul Manafort, ninety per cent of self-identified Republicans said that they approve of the job the President is doing. Unless this figure drops precipitously, it is difficult to see twenty Republicans voting against him in an impeachment trial. (Assuming all the members of the Democratic caucus voted against Trump, that is how many defectors it would take for a two-thirds majority in the Senate.) But approval ratings—even Trump’s—can change in response to dramatic developments. Mueller hasn’t fully revealed his hand, the power structure on Capitol Hill is about to shift, and the man Trump wanted at his side in the White House has balked. No wonder Trump is back to tweeting “WITCH HUNT.”