Mr. Trump, his daughter Ivanka and his son-in-law, Jared Kushner, suspected Mr. Priebus of being a leaker and had been looking to knife him in the back for a while. In Mr. Scaramucci, a self-described “front-stabbing person,” they had their man.

Never mind that the Mooch had called Mr. Trump “another hack politician” during the campaign and supported two of his challengers. He loved Mr. Trump, he told reporters during his first press conference, just maybe because he won. “I think there’s been, at times, a disconnect between the way we see the president and how much we love the president, and the way some of you perhaps see the president,” he said, blowing a kiss as he left the lectern.

Mr. Scaramucci had previously failed to secure several Trump administration positions, but not for lack of trying. He was rejected for the position of White House public liaison after he had trouble resolving potential conflicts of interest stemming from his agreement to sell his company, SkyBridge Capital, to a Chinese conglomerate with ties to the government in Beijing. He was named ambassador to the Organization for Economic Cooperation and Development. While still awaiting Senate confirmation for that job, he was appointed chief strategy officer of the United States Export-Import Bank, an institution Mr. Trump called “excess baggage” during the campaign. But what he really wanted was to dive into the White House mosh pit.

This was all clearly heady stuff for the Mooch. Once he was appointed, he deleted all tweets criticizing Mr. Trump from his Twitter account while proclaiming “full transparency.” He said his about-face on Mr. Trump made him like Winston Churchill and Ronald Reagan, “some of the greatest leaders known to mankind” who have “changed and evolved and adapted.” He tweeted photos of himself, himself with Mr. Trump, himself with White House staffers, and his seat-assignment place card from aboard Air Force One. He retweeted a “Daily Show” bit mocking him for imitating Mr. Trump’s hand gestures.

But last Wednesday, the Mooch made the after-hours phone call that would bring it all crashing down. In a bonkers colloquy with The New Yorker’s Ryan Lizza, a raving Mr. Scaramucci used colorful and profane language to call Stephen Bannon, Mr. Trump’s chief strategist, a self-promoter. He vowed to “kill all the leakers,” especially Mr. Priebus, accusing Mr. Priebus of — horrors — leaking the fact that Mr. Trump and the first lady had dinner with the former Fox News boss Bill Shine and Sean Hannity, Fox talker and Trump sycophant. Working himself into a lather, Mr. Scaramucci said, and later tweeted, that he’d called the F.B.I. and the Department of Justice to report “a felony” after his financial disclosure report was “leaked” — by Mr. Priebus, he suspected — to a reporter. He tried to walk that back after learning that the report was publicly available. Then came his Cain and Abel interview the next morning.