Representative Devin Nunes looked uneasy. Mr. Nunes, the chairman of the House Intelligence Committee, was struggling on Monday to elicit details from James Comey, the F.B.I. director, about his explosive revelation that the bureau is investigating whether Russia and the Trump administration colluded to sabotage Hillary Clinton’s presidential candidacy. That disclosure, Mr. Nunes said, had put “a big, gray cloud” over the White House.

On Wednesday, Mr. Nunes tried to replace that cloud with a smoke screen. In a possible violation of the law, Mr. Nunes described intelligence reports that he said had suggested that American intelligence agencies incidentally intercepted communications of then President-elect Trump and people close to him, and then disseminated the information widely throughout the intelligence community. His disclosures, which have destroyed the credibility of his committee in investigating Russian interference in the election, make clear that he is unfit for the job and should be replaced.

Mr. Nunes’s remarks, which appeared to be deliberately vague, gave President Trump cover for his baseless claim that President Barack Obama had illegally wiretapped his phones. After making his disclosures during a news conference on Wednesday, Mr. Nunes went to the White House to brief the president. In a startling break with tradition, Mr. Nunes, a Republican, briefed reporters before sharing his findings with fellow members of the committee, who are from both parties. Mr. Trump portrayed the congressman’s assertions as a vindication of his widely discredited accusation. “I very much appreciated the fact that they found what they found,” Mr. Trump said.