As White House aides scrambled to figure out how to respond, Mr. Trump recalled that Mr. Bolton once told him he wanted to be national security adviser because he worried he couldn’t win the Senate confirmation required for many other senior jobs.

“I should have seen that as a red flag,” Mr. Trump said, according to an aide in the room. “But instead, I did the guy a favor, took him at his word that this was a good fit, and this is what he did to me?”…

On Tuesday afternoon, all 53 Republican senators gathered in an ornate room near the Capitol Rotunda. Mr. McConnell was clutching a card—apparently a tally of Republican votes on the witness question—marked with “yeses,” “noes” and “maybes.”

He told them the vote count wasn’t where it needed to be, according to people familiar with the meeting, and struck an ominous tone, saying the future of the country and the Constitution were at stake. People close to Mr. McConnell were struck by his intensity. They felt that he had moved the needle.