Updated on March 20 at 5:46 p.m. ET

With just two sentences on Monday, FBI Director James Comey cast a long, dark shadow over the presidency of Donald Trump and the campaign that resulted in his election.

“I’ve been authorized by the Department of Justice to confirm that the FBI, as part of our counterintelligence mission, is investigating the Russian government's efforts to interfere in the 2016 presidential election,” Comey said in testimony before the House Intelligence Committee. “That includes investigating the nature of any links between individuals associated with the Trump campaign and the Russian government, and whether there was any coordination between the campaign and Russia’s efforts.”

Comey’s declaration was not a surprise; reports about a federal probe involving Trump have been swirling for months. But his decision to publicly confirm that the sitting president’s campaign is under investigation for possibly colluding with a foreign power to undermine an election was a stunning revelation, and one whose significance both Democrats and Republicans immediately recognized.

“By your announcement today, there is now a cloud that undermines our system,” Representative Michael Turner, an Ohio Republican, pointedly told the FBI director. Under questioning, Comey said that the FBI began the investigation in late July. That disclosure will likely inflame Democratic criticism that Comey chose to publicly discuss the bureau’s inquiry into Hillary Clinton’s emails during the closing days of the 2016 election but did not reveal it was also investigating the Trump campaign and Russian meddling.

Comey’s confirmation of an ongoing investigation was just one of several statements that amounted to an extraordinary rebuke of a president who has the power to remove him from office. He directly refuted Trump’s repeated claims that former President Barack Obama “wiretapped” him at Trump Tower, a charge that the White House has been unable to provide evidence for.

“I have no information that supports those tweets,” Comey told Representative Adam Schiff of California, the top Democrat on the committee who had read several of Trump’s charges aloud to him. He went on to explain that he had surveyed his entire department and was told that the answer was “the same for the Department of Justice and all its components: The department has no information that supports those tweets.”

At one point, Schiff asked Comey about Trump’s accusation that the president’s critics in the government were engaging in a witch-hunt akin to Joseph McCarthy’s crusade against Communists in the 1950s. “Were you engaged in McCarthyism, Director Comey?” the congressman asked.

“I try very hard not to engage in any ’isms of any kind, including McCarthyism,” Comey replied, to laughter from the hearing room.

At the president’s behest, the White House has stood by Trump’s claims, and hours before the hearing, he vented his frustration at the scrutiny with a sort-of prebuttal of the congressional hearing on Twitter. “James Clapper and others stated that there is no evidence Potus colluded with Russia,” Trump wrote, referring to the former director of national intelligence. “This story is FAKE NEWS and everyone knows it!”

Trump (or his aides) also responded to the hearing in real-time, tweeting clips to buttress the president’s argument. One tweet—sent by the official @POTUS account rather than Trump’s more frequently-deployed personal one—linked to an exchange between Comey and GOP Representative Trey Gowdy of South Carolina. The heading: “FBI Director Comey refuses to deny he briefed President Obama on calls made by Michael Flynn to Russia.” Trump also tweeted links to testimony in which Comey and NSA Director Michael Rogers said they had no evidence that Russia’s meddling directly changed votes in the election as well as Rogers’s warning that leaking classified information threatens national security.

Yet while Rogers and Comey said that Russia had not hacked into voting machines, they repeatedly stood by their conclusions that Russia had interfered with the election in an attempt to help Trump and hurt Clinton.

The hearing lasted more than five hours, enough time for one Democratic lawmaker, Representative Jim Himes of Connecticut, to ask Comey and Rogers about a tweet Trump had sent while they were testifying that asserted, “The NSA and FBI tell Congress that Russia did not influence electoral process.” The FBI director appeared briefly taken aback.

“I haven’t been following anybody on Twitter while I’ve been sitting here,” he told Himes. But when the congressman read what the president had said, Comey refuted that one, too. “It certainly wasn’t our intention to say that today, because we have no information on that subject,” he said.

Aside from his comments on the president’s tweets, Comey refused to discuss specifics of the FBI’s investigation or to fact-check anonymously-sourced reports of its findings in the press—a limitation that proved frustrating to lawmakers in both parties. As the hearing proceeded, a pattern developed in the questioning that reflected the respective political priorities for Republican and Democratic members of the intelligence committee.

Protecting the White House, GOP lawmakers pressed Comey on the danger of leaking details of investigations and surveillance to national security and pressed him on whether the FBI would prosecute officials who disclosed classified information about Trump officials, particularly the former national security adviser Michael Flynn. Democrats focused on the investigation itself.

Though Comey warned lawmakers he would not discuss specific officials, Democrats asked him about former Trump campaign manager Paul Manafort and his ties to Russian oligarchs, along with Trump adviser Roger Stone and his contacts with Guccifer 2.0, the hacker that took credit for infiltrating the email accounts of the Democratic National Committee and John Podesta, Clinton’s campaign chairman. “I’m not going to talk about any particular person here today,” Comey said in reference to Stone.

Several Republicans tried to get Comey to confirm which top Obama administration officials would have had access to classified material related to the FBI’s investigation or U.S. intelligence gathering, an apparent attempt to narrow down who might have leaked details of the inquiry to reporters. Gowdy specifically asked about former Attorney General Loretta Lynch, National Security Adviser Susan Rice, and CIA Director John Brennan.

Comey held fast to a policy of not rebutting inaccurate press reports for fear of disclosing classified information to allies simply by virtue of denying them. While he declined to discuss any Obama administration officials specifically, he did acknowledge that people claiming access to secret material had been commenting about it to reporters “in ways that have struck me as unusually active.”

And Comey did advocate aggressive prosecution of government leakers to the point of handing down prison terms. “We don’t talk about it because we don’t want to confirm it,” he said of press reports that rely on classified material. “But I do think it should be investigated aggressively and if possible prosecuted so people take as a lesson this is not okay. This behavior can be deterred, and it’s deterred by locking some people up who have engaged in criminal activity.”

Democrats sought mostly to build their own case against the president and his associates, irrespective of what Comey was willing to discuss. Time and again, they used their questioning time to enter into the record public reports about Manafort, Stone, Flynn, and Attorney General Jeff Sessions, all of whom are presumably part of the FBI investigation. And almost without fail, Comey refused to discuss them.

Asked directly whether Trump himself was a target of the investigation, the FBI director demurred.

One question that Democrats curiously chose not to ask Comey, however, centered on his own decision to discuss the FBI’s inquiry into the Clinton email server before the election while not disclosing that the bureau was, beginning in late July, investigating the Trump campaign’s connection to a foreign power. The director appeared to allude to the comparison in his opening statement, when he said the FBI sometimes is more forthcoming about investigations that have been completed as opposed to those that are open. He sent Congress a letter about the Clinton probe last October to inform lawmakers that investigators were looking at additional emails after he earlier indicated the investigation has ended.

Not only did Comey not inform the public about the Trump investigation last year, he didn’t tell senior congressional leaders. Under questioning from GOP Representative Elyse Stefanik of New York, the director said it was his custom to advise a bipartisan group of top lawmakers about “sensitive” investigations on a quarterly basis. But Comey said that because the Russia inquiry was so sensitive, he did not tell either the leadership or senior members of the intelligence committees about the investigation until recently—months after the FBI began its investigation in late July.

That didn’t sit well with either Stefanik or Representative Devin Nunes of California, the committee chairman. Asked by reporters after the hearing if he accepted Comey’s explanation, Nunes replied: “No, I don’t.” He added: “Had we known about this back in July, clearly we wouldn’t be in this position today.”

Though Comey was not pressed on his decision to keep the Trump investigation quiet, he expressed regret about the FBI’s initial response to the hacking of the Democratic National Committee’s email server. The DNC took months to adequately assess the security threat, a lapse in part blamed on a lack of urgency on the part of the FBI in warning them their system had been compromised. By then, it was too late. “I might have walked over there myself knowing what I know now,” Comey said.

For Republicans, the revelations from Comey seemed almost too troubling to believe. Members of the committee pressed him and Rogers to substantiate their conclusion—and that of the intelligence community as a whole—that Putin intervened not merely to mess with the United States but with the goal of electing Trump.

“Mr. Putin would like people who like him,” Comey said at one point, by way of explaining why the Russian president might prefer Trump. He said it was well-known that Putin respects business leaders, citing former German Chancellor Gerhard Schroder and former Italian Prime Minister Silvio Berlusconi as examples. “He believes they're people that are more open to negotiation, easier to deal with,” Comey said of Putin.

Nunes and other GOP committee members implored him to expedite the investigation, if only to clear the names of Trump administration officials and campaign advisers who have been linked to the probe in press reports. “There is a big gray cloud that you’ve now put over people who have very important work to do leading this country,” Nunes said. “So the faster you can get to the bottom of this, the better it will be for all Americans.”

For Democrats, the feeling of a Comey-created cloud was familiar. It was less than a a year ago that his statement criticizing Clinton for her “extremely careless” handling of a private email server—even while clearing her of criminal wrongdoing—altered the dynamic of the presidential campaign. And his subsequent letter to Congress just 10 days before the election, they now believe, might have led directly to her defeat.

On Monday, Democrats had no difficulty accepting Comey’s testimony about Russia, but their assessment of its implications were far more grave. “We’ve heard nothing but terribly disturbing evidence of what’s happened to our country at the hands of arguably our greatest adversary,” said Representative Denny Heck, a Democrat from Washington state. He then asked Comey and Rogers to put into their own words why the FBI’s investigation into Russian meddling is important, and why the public should care that the men and women who now lead the country just might have been involved.

“It threatens what is America,” Comey replied, “and if any Americans are a part of that effort, it’s a very serious matter.”