WASHINGTON — Upset about the investigation into Russian interference in last year’s election, President Trump sought relief from James B. Comey, then the F.B.I. director. By Mr. Comey’s account, Mr. Trump asked him to help “lift the cloud.”
But thanks to Mr. Trump’s own actions, the cloud darkened considerably on Thursday and now seems likely to hover over his presidency for months, if not years, to come.
Rather than relieve the pressure, Mr. Trump’s decision to fire Mr. Comey has generated an even bigger political and legal threat. In his anger at Mr. Comey for refusing to publicly disclose that the president was not personally under investigation, legal experts said, Mr. Trump may have actually made himself the target of an investigation.
While delivered in calm, deliberate and unemotional terms, Mr. Comey’s testimony on Thursday was almost certainly the most damning j’accuse moment by a senior law enforcement official against a president in a generation. In a Capitol Hill hearing room, the astonishing tableau unfolded of a former F.B.I. director accusing the White House of “lies, plain and simple” and asserting that when the president suggested dropping an investigation into his former national security adviser, “I took it as a direction.”
Mr. Comey gave ammunition to the president’s side, too, particularly by admitting that he had orchestrated the leak of his account of his most critical meeting with Mr. Trump with the express purpose of spurring the appointment of a special counsel, which he accomplished. The president’s defenders said Mr. Comey had proved Mr. Trump was right when he called the former F.B.I. director a “showboat” and a “grandstander,” a conclusion Democrats once shared when he was investigating Hillary Clinton last year.
But Mr. Comey also revealed that he had turned over memos of his conversations with Mr. Trump to that newly appointed special counsel, Robert S. Mueller III, suggesting that investigators may now be looking into whether Mr. Trump obstructed justice by dismissing the F.B.I. director.
“This was a devastating day for the Trump White House, and when the history of the Trump presidency is written, this will be seen as a key moment,” said Peter H. Wehner, who was White House adviser to President George W. Bush. “My takeaway is James Comey laid out facts and was essentially encouraging Mueller to investigate Trump for obstruction. That’s a huge deal.”
The White House was left in the awkward position of trying to minimize the damage. Mr. Trump himself remained uncharacteristically silent, while his advisers kept the daily briefing off camera and sent out the backup to Sean Spicer, the press secretary. “I can definitively say the president is not a liar,” Sarah Huckabee Sanders, the principal deputy press secretary, told reporters.
Washington has not seen a spectacle quite like this since the days of Watergate, Iran-contra or President Bill Clinton’s impeachment. Whatever the controversies under Mr. Bush and President Barack Obama, neither was ever accused of personal misconduct by a current or former law enforcement official in such a public forum.
Indeed, Mr. Comey highlighted the difference by noting that he had never taken notes of his conversations with either of those presidents because he trusted their basic integrity, but he did write memos about each of his one-on-one encounters with Mr. Trump because “I was honestly concerned that he might lie about the nature of our meeting.”
In any other presidency, the events laid out by Mr. Comey — Mr. Trump asking for “loyalty” from the F.B.I. director who was investigating the president’s associates, then asking him to drop an investigation into a former aide and ultimately firing him when he did not — might have spelled the end.
But Mr. Trump has tested the boundaries of normal politics and upended the usual rules. To his supporters, the inquiries are nothing more than the elite news media and political establishment attacking a change agent who threatens their interests.
“This is like an explosive presidency-ending moment,” said John Q. Barrett, a law professor at St. John’s University in New York and an associate independent counsel during the Iran-contra investigation in Ronald Reagan’s presidency. “But we have a different context now.”
The articles of impeachment drafted against President Richard M. Nixon and Mr. Clinton both alleged obstruction of justice, in effect making clear that such an action could qualify under the “high crimes and misdemeanors” clause of the Constitution. The “smoking gun” tape that doomed Mr. Nixon in 1974 recorded him ordering his chief of staff to have the C.I.A. block the F.B.I. from investigating the Watergate burglary. Critics said that Mr. Trump’s comments to Mr. Comey effectively cut out the middle man.
The House impeached Mr. Clinton in 1998 for lying under oath and obstructing justice to cover up his affair with Monica Lewinsky, a former White House intern, during a sexual harassment lawsuit. The obstruction alleged in Mr. Clinton’s case was persuading Ms. Lewinsky to give false testimony, advising her to hide gifts he had given her to avoid any subpoena and trying to find her a job to keep her happy. After a trial, the Senate acquitted him.
As a political matter, both Mr. Nixon and Mr. Clinton faced a House under control of the opposition party, while Mr. Trump has the benefit of a Republican House that would be far less eager to open an impeachment inquiry. And for all of the fireworks on Thursday, the reaction in Congress still broke down largely along partisan lines, with Democrats in attack mode and Republicans either defending Mr. Trump or remaining silent. That may leave the question to Mr. Mueller.
“The polarization seems even worse than during the Lewinsky investigation, which I hadn’t thought possible,” said Stephen Bates, an associate independent counsel during the investigation into Mr. Clinton. “Everyone gets judged in terms of helping or hurting Trump. Whatever Mueller does, half of the country will call him courageous and half will call him contemptible. We just don’t know which half is which.”
The defense on Thursday was left to Mr. Trump’s personal lawyer, Marc E. Kasowitz, who selectively used Mr. Comey’s testimony, disputing the damaging parts while citing the parts he considered helpful. He denied that the president had ever asked Mr. Comey for loyalty or to let go of the investigation into Michael T. Flynn, the former national security adviser. But he cited Mr. Comey’s statement that the president himself was not under investigation at the time the F.B.I. director was fired.
He also assailed Mr. Comey for leaking details of his conversations with the president to prompt the appointment of a special counsel, although they were not classified. “It is overwhelmingly clear that there have been and continue to be those in government who are actively attempting to undermine this administration with selective and illegal leaks of classified information and privileged communications,” he said. “Mr. Comey has now admitted that he is one of these leakers.”
Tellingly, the Republicans on the Senate Intelligence Committee paid no heed to the talking points distributed in advance by the Republican National Committee at the behest of the White House. Instead of attacking Mr. Comey’s credibility, as the R.N.C. and Donald Trump Jr. did, the Republican senators praised him as a patriot and dedicated public servant. They largely accepted his version of events, while trying to elicit testimony that would cast Mr. Trump’s actions in the most innocent light possible.
Mr. Comey cooperated to some extent by trying not to go too far beyond the facts as he presented them, declining, for instance, to say whether he thought Mr. Trump’s statements amounted to obstruction of justice.
“In a credibility battle between Trump and Comey, everybody knows Comey is going to win that war,” said Adam W. Goldberg, who was an associate special White House counsel under Mr. Clinton during Kenneth W. Starr’s investigation.
For Mr. Trump, the battle with Mr. Comey now overshadows much of what he wants to do. Major legislation is stalled. Mr. Kasowitz said the president was “eager to continue moving forward with his agenda, with the business of this country, and with the public cloud removed.”
For now, though, the cloud remains.