Just before 3:20 on Monday afternoon, Devin Nunes, the Republican head of the House Intelligence Committee, asked James Comey, the director of the Federal Bureau of Investigation, who was testifying before the committee on his agency’s investigation into Russian interference in last year’s Presidential election, a last set of questions. Earlier in the hearing, Nunes, seemingly taking his lead from a series of early-morning tweets by President Trump, had focussed his questions on the leaks of classified information that have plagued the Administration since January. Now, though, Nunes got to the crux of the matter: Comey's public confirmation that the F.B.I. was investigating possible coördination between people associated with the Trump campaign and Russia.

Nunes asked Comey if he had evidence that anyone currently working in the Trump Administration had undisclosed ties to Russia. Comey refused to answer. Nunes tried again: What about Kellyanne Conway? "Same answer," Comey said. Nunes didn't pretend to be surprised. "There is a big gray cloud you have put over the people who lead this country," he went on. "The faster you can get to the bottom of this, it's going to be better for all Americans."

It was a statement rather than a question, but Comey evidently felt obliged to respond. "I understand," he said, quietly.

Thus ended a hearing the likes of which Washington hasn't seen in many a day—if, indeed, there has ever been anything like it. It lasted five hours and twenty minutes, with just a single bathroom break, and while it began with Comey’s acknowledgement that an investigation existed, much of the rest of it was taken up with his refusals to provide any more details about the probe, or to comment on individual Trump associates whom media reports have tied to it. "I know that is extremely frustrating to some folks," he said, in his opening statement. "I hope you and the American people can understand. The F.B.I. is very careful in how we handle information about our cases and about the people we are investigating."

Despite his reticence, Comey said more than enough to transfix the political world, and to leave many Republicans feeling as helpless as supporters of Hillary Clinton felt in October, when Comey revealed that the F.B.I. had reopened its investigation into Clinton's private e-mail server.

Despite refusing to go into specifics, Comey did point out that, "as with any counterintelligence investigation, this will also include an assessment of whether any crimes were committed." Arguably, he didn't need to say that: investigating possible crimes is what the F.B.I. does. Evidently, though, Comey felt it was necessary to explain to the public why the F.B.I. had made the unprecedented decision to launch a counterintelligence investigation into a major party’s Presidential candidate.

At one point, Michael Turner, a Republican congressman, quizzed Comey on this very question: What does it take for the F.B.I. to open a counterintelligence investigation? He only succeeded in getting Comey to confirm that the agency doesn't act lightly.

“What is the tipping point?” Turner asked. “Don’t you need some action or some information besides just attending a meeting, having been paid to attend a conference, that a picture was taken or that you travelled to a country, before you open an investigation for counterintelligence by the F.B.I.?” Comey said that a couple of things could come into play: “a credible allegation of wrongdoing or reasonable basis to believe that an American may be acting as an agent of a foreign power.”

If that weren’t bad enough for the White House, Comey also spoke openly, and at length, about Russian interference in the election, and he defended the intelligence community's judgment that Vladimir Putin sought to tip the scales in Trump's favor.

Congressman Adam Schiff, the ranking Democrat on the panel, first got Comey to say that the Russian government preferred a candidate who had a dim view of NATO, and that it hoped to see the lifting of sanctions that were imposed after the Russian invasion of Crimea. Then Schiff asked Comey whether the Russians would "have a preference for a candidate who expressed open admiration for Putin." After pausing for a moment, Comey replied, "Can I help you reformulate the question? Mr. Putin would like people who like him."

In an exchange with Mike Conaway, a Texas Republican, Comey said that, by early December of 2016, the F.B.I. had come to the conclusion that Russia had wanted to undermine faith in America’s election process, and that it had sought to denigrate Clinton and hurt her campaign. "The conclusion that active measures were taken specifically to help President Trump's campaign, you had that—by early December, you already had that conclusion?" Conaway asked.

"Correct, that they wanted to hurt our democracy, hurt her, help him," Comey replied. "I think all three we were confident in, at least as early as December."

Comey also informed the committee that the F.B.I.'s investigation into the Trump campaign began in July, 2016. Perhaps surprisingly, it was a Republican, Elise Stefanik, who represents a district in upstate New York, who asked Comey why he hadn't informed lawmakers earlier. "Because of the sensitivity of the matter," Comey replied

That answer didn't satisfy Stefanik, and it won't satisfy many Democrats, who are still furious at Comey for, in their view, helping to tip the election in Trump's favor with his announcement about the Bureau’s Clinton investigation. In this instance, though, it is Republicans who have reasons to be gravely concerned about what the F.B.I. director said.

As the hearings wore on, some of the Party's representatives wisely departed from the smoke-screen strategy of talking about leaks, and pointed to a statement made last month by James Clapper, President Obama's director of national intelligence. Speaking on "Meet the Press,” Clapper said that, when he left the government, he hadn't been aware of any evidence of "collusion" between members of the Trump campaign and Russian officials.

Comey, responding to Pete King, the veteran Republican congressman from Long Island, said that Clapper’s remarks were "not something I can comment on." Mike Quigley, an Illinois Democrat, tried to get him to discuss the meaning of collusion, and the difference between implicit and explicit collusion. Once again, Comey refused to be drawn in. "Collusion is not a term, a legal term of art," he said, "and it's one I haven't used here today, as we're investigating to see whether there was any coördination between people associated with the campaign—” Quigley cut Comey off before he could say "the Russians," but his meaning was clear.

In case it wasn't, he spelled it out to Denny Heck, a Democrat from Washington State, who asked Comey to explain to the American people "why we should care about Russia's use of U.S. persons, of Americans, helping Russia destabilize our democracy." Comey, who earned his reputation for independence when he worked in George W. Bush's Justice Department, began by saying that he "truly believed" that America is a "shining city on a hill," in the words of Ronald Reagan.

He went on, "One of the things we radiate to the world is the importance of our wonderful, often messy, but free and fair democratic system, and the elections that undergird it. So when there is an effort by a foreign nation-state to mess with that, to destroy that, to corrupt that, it is very, very serious. It threatens what is America. And if any Americans are part of that effort it's a very serious matter. And so you would expect the F.B.I. to want to want to understand, is that so? And, if so, who did what?"

It was for these reasons, Comey said, that he had decided it was important to share at least some information about the investigation with the committee and the American people. "And now we are going to close our mouths and do our work to see if we can answer those questions," he continued. "Because the answers matter."