“I think you’re going to find some very interesting items coming to the forefront over the next two weeks,” Mr. Trump said.

Monday, March 20

At the first public hearing in the House investigation, James B. Comey, the director of the F.B.I., took the extraordinary step of announcing that the agency is investigating possible collusion between members of Mr. Trump’s campaign and Russian officials.

Mr. Comey also dismissed Mr. Trump’s claim that he was wiretapped.

Tuesday, March 21

Sometime that day — the precise timing remains unclear — Mr. Nunes received a call from a person he has described only as a source. The call came as he was riding across town with a staff member in an Uber vehicle. Mr. Nunes quickly got out of the car and went to the White House. There, he has said he reviewed “dozens” of intelligence reports.

Wednesday, March 22

At a hastily arranged news conference, Mr. Nunes revealed he had received information about the incidental intelligence collection by American spy agencies, saying he could discern the identities of Trump associates from reading reports about intercepted communications, which were shared among Obama administration officials with top security clearances. He refused to identify sources, suggesting they were whistle-blowers trying to expose wrongdoing at great risk to themselves.

Mr. Nunes then dashed off to the White House to brief Mr. Trump on what he had learned the day before and followed up that meeting with an impromptu news conference in the driveway of the White House. There, he stressed that while the new information did not validate Mr. Trump’s wiretapping claim, it did show that the president might have been correct to say he had been surveilled.

Around the same time, Mr. Trump was asked by reporters if he felt vindicated. “I somewhat do,” he said. “I must tell you I somewhat do.”

Around 5 p.m., Representative Adam B. Schiff of California, the top Democrat on the Intelligence Committee, held his own news conference denouncing Mr. Nunes for briefing Mr. Trump before talking to members of his own committee.