But a subsequent memo by Democrats on the House Intelligence Committee undercut those claims, revealing that law enforcement officials had been forthcoming about their sources of the information they cited in seeking permission to surveil Mr. Page.
Conservatives nonetheless seized on the Republican document, which officials at the Justice Department and the F.B.I. said omitted key facts, as grounds for demanding Mr. Rosenstein’s head.
The Tea Party Patriots, a political group, produced a dramatic TV ad calling him “a weak careerist at the Justice Department, protecting liberal Obama holdovers and the ‘deep state’ instead of following the rule of law,” and calling on him to do his job or resign. In April, Mr. Trump lashed out at Mr. Rosenstein for having “signed a FISA warrant,” an apparent reference to Mr. Rosenstein’s role in the surveillance request.
Known as a meticulous lawyer, Mr. Rosenstein began his career at the Justice Department in 1990 as a trial lawyer in the public integrity section of the criminal division in Washington, and rose through the ranks to be nominated in 2005 by President George W. Bush as the United States attorney in Maryland. He held that post for a dozen years, throughout the Obama administration, before being confirmed by the Senate last year as the deputy attorney general.
Within a month, he had been swept into the turmoil surrounding Mr. Comey’s firing when Mr. Trump cited a three-page memo Mr. Rosenstein wrote as a pretext for the sudden dismissal. The memo blamed Mr. Comey’s handling in 2016 of the investigation into Hillary Clinton’s use of a private email server while she was secretary of state.
But Mr. Rosenstein had told lawmakers that he knew that Mr. Comey was to be ousted before he ever sat down to write his memo, and days before, he had spoken with a member of the White House Counsel’s Office about how to handle the matter. Soon after Mr. Comey was fired in May of 2017, Mr. Trump and aides began offering varying explanations, with the president admitting within days that he had made the decision himself as he fumed about the investigation Mr. Comey was leading into his campaign’s ties with Russia.
The day after Mr. Comey’s firing, in an at times tense conversation with Donald F. McGahn II, the White House counsel, Mr. Rosenstein stressed that he did not want to be part of an effort to obfuscate or “massage” the facts about it, according to a person with knowledge of the discussion.