Deputy Attorney General Rod Rosenstein. AP Photo/Patrick Semansky Deputy Attorney General Rod Rosenstein told senators in a closed-door briefing Thursday that he knew FBI Director James Comey would be fired before he wrote a memo outlining his mishandling of the investigation into Hillary Clinton's use of a private email server, a top Democratic senator said.

Sen. Claire McCaskill of Missouri told reporters gathered outside the briefing room that Rosenstein had "acknowledged that he learned Comey would be removed prior to him writing his memo," despite the White House initially insisting that Trump fired Comey on Rosenstein's recommendation.

Trump fired Comey on May 9.

Democratic Sen. Dick Durbin told reporters that he did not think Rosenstein was pressured to write the memo, but he said Rosenstein told the senators that he knew the day before Comey was fired that Trump intended to dismiss him.

That conflicts with White House press secretary Sean Spicer's explanation in the immediate aftermath of Comey's firing that it "was all" Rosenstein's idea.

"This was a DOJ decision," Spicer told reporters on May 9, referring to the Department of Justice. White House deputy press secretary Sarah Huckabee Sanders told reporters the next day that the letters Trump received on Tuesday outlining "the basic atrocities" Comey committed "in circumventing the chain of command of the Department of Justice" persuaded him to fire the director.

On May 10, Vice President Mike Pence also said Trump had based his decision on Rosenstein's recommendation.

That explanation quickly unraveled, however, as reports surfaced that Trump decided he would fire Comey nearly a week before Rosenstein wrote the memo.

In an interview with NBC's Lester Holt on May 11, Trump said he was going to fire Comey "regardless" of the recommendations of Rosenstein and Attorney General Jeff Sessions. He called Comey "a showboat" and "a grandstander" and said he fired the director because the FBI was in "turmoil." (Acting Director Andrew McCabe denied that the bureau had lost faith in Comey.)

During a press conference that day, however, Trump appeared to fall back on the White House's talking point that he had fired Comey at Rosenstein's recommendation.

Rosenstein reportedly threatened to resign — after two weeks on the job — because he was made to be the administration's scapegoat. The Justice Department denied that Rosenstein had made the threat, but the White House ultimately shifted the responsibility off Rosenstein.

"After watching Director Comey's testimony last Wednesday, the president was strongly inclined to remove him," the White House said on May 11 as part of what it said was a timeline of the president's decision-making process.

Matthew Miller, a former spokesman for the Justice Department who has been critical of Trump, tweeted on Thursday that Rosenstein's admission was "terrible" because it showed that he "completely compromised DOJ's independence & his integrity."

"A real blow to the department," Miller said, before questioning whether Rosenstein knew when he agreed to write the memo that Trump had asked Comey to end the investigation into Michael Flynn, the former national security adviser. (Comey reportedly wrote a memo about the incident, which he shared with top FBI officials.)

Susan Hennessey, a former lawyer for the National Security Agency, agreed that Rosenstein's admission was terrible but said it was "a good sign he acknowledged it directly in congressional testimony and did not decline to answer or otherwise obfuscate."