But to the president’s most ardent supporters, Mr. Nunes is a hero.

“The vindication of Devin Nunes continues,” Representative Matt Gaetz, Republican of Florida, said in an interview Thursday. Noting that the House Ethics Committee recently cleared Mr. Nunes of allegations he mishandled classified information, Mr. Gaetz went on: “He’ll be even more vindicated as the public learns more about the abuses at the F.B.I. and the Department of Justice.”

Mr. Ryan, for his part, waved off any suggestion of removing Mr. Nunes.

“He’s focusing on keeping our country safe, focused on national security,” he told reporters here at the Greenbrier resort, where congressional Republicans are gathered for their annual retreat. He accused Democrats of playing “some political game” to divert attention from tax cuts and a strengthening economy.

A spokesman for Mr. Nunes did not respond to messages seeking comment.

Mr. Nunes, 44, has made an unlikely transition from a leadership loyalist who once heaped scorn on Republican hard-liners to one of the hard-liners’ idols. His “lemmings” comment came in 2013 as Senator Ted Cruz, Republican of Texas, and the conservative House Freedom Caucus were pressing to shut down the government unless President Barack Obama agreed to stop all funding for the Affordable Care Act. At that time, he was quick with a quip to dismiss his party’s impractical right flank.