“That’s a conclusion I’m sure the special counsel will work towards, to try and understand what the intention was there and whether that’s an offense,” Mr. Comey said.
Firing Mr. Comey ignited an unexpected political fire for the president, and Mr. Comey acknowledged helping fan the flames. He said he had encouraged a friend to give The New York Times details from one of his memos, a move he hoped would lead to the appointment of a special counsel. It did.
Before firing Mr. Comey, Mr. Trump was dogged by the F.B.I. inquiry into his campaign’s ties to Russia. But he was never personally under investigation.
Now, he faces the prospect of an obstruction investigation, inquiries by emboldened congressional officials and questions from both parties about whether he tried inappropriately to end the F.B.I. inquiry into Michael T. Flynn, his former national security adviser.
Mr. Trump’s personal lawyer, Marc E. Kasowitz, flatly denied any obstruction. “The president never, in form or substance, directed or suggested that Mr. Comey stop investigating anyone,” he said.
But Mr. Kasowitz’s involvement was itself a reflection of how Mr. Comey’s firing had deepened the president’s political and legal difficulties. Mr. Trump hired him recently to help contain the fallout.
The Senate hearing did not help that effort. It was the most highly anticipated and crowded congressional event in recent memory.
Over a long career, Mr. Comey has excelled at telling his story while tiptoeing around Washington’s bureaucratic minefields. He has been so at ease before Congress that some staff members have jokingly called him “Senator Comey.” But this time, he offered more frank, emotional introspection than he had before.
He set that tone from the beginning, opening with a goodbye to his former employees, to whom he was unable to personally bid farewell. And he said Mr. Trump had lied — a word that is often soft-pedaled in Washington — when he justified the firing by saying Mr. Comey had lost the confidence of an F.B.I. in disarray. “Those were lies, plain and simple,” Mr. Comey said.
He said the president had defamed him, an apparent reference to Mr. Trump’s calling him a “nut job” in a private meeting with Russian diplomats.
And when Republicans asked why he had not told the president he was out of line for asking Mr. Comey to “see your way clear to letting this go, to letting Flynn go,” Mr. Comey said perhaps he should have.
“I don’t want to make you — sound like I’m Captain Courageous,” he replied. “I don’t know whether, even if I had the presence of mind, I would have said to the president, ‘Sir, that’s wrong.’”
But he said he had no doubt about Mr. Trump’s intentions. “I took it as a direction,” he said. If the president had his way, Mr. Comey said, “we would have dropped an open criminal investigation.”
Mr. Comey’s testimony forced Mr. Trump’s supporters into the uncomfortable position of drawing a distinction between suggesting that the F.B.I. close an investigation into a friend and outright ordering it.
“Knowing my father for 39 years when he ‘orders or tells’ you to do something there is no ambiguity, you will know exactly what he means,” the president’s son Donald Trump Jr. wrote on Twitter during the hearing.
Mr. Mueller, the special counsel, is investigating Mr. Flynn along with the broad question of whether the Trump campaign helped Russian operatives meddle in the presidential election. Next week, as part of a separate investigation, the Senate Intelligence Committee’s staff will interview Jared Kushner, the president’s adviser and son-in-law, Senator Angus King, independent of Maine, said Thursday night.
Mr. Comey placed the origins of the special counsel investigation squarely on Mr. Trump’s Twitter account, a frequent source of conflict for the president. Two days after Mr. Comey was ousted, The Times reported that Mr. Trump had asked Mr. Comey to pledge loyalty to him. The president then tweeted that Mr. Comey had “better hope that there are no ‘tapes’” of their meetings.
That tweet inspired Mr. Comey to allow a friend to read portions of his memo to The Times. A day after The Times revealed the contents of that memo, which described the conversation about Mr. Flynn, the Justice Department appointed Mr. Mueller to take over the investigation.
The White House has not commented on whether recordings exist. But Mr. Comey repeatedly baited Mr. Trump to produce them if they did. “Lordy, I hope there are tapes,” he said at the hearing. “The president surely knows if there are tapes. If there are, my feelings aren’t hurt. Release the tapes.”
Mr. Trump has offered changing reasons for firing Mr. Comey. The White House originally cited Mr. Comey’s handling of last year’s investigation into Hillary Clinton’s use of a private email server, saying Attorney General Jeff Sessions and the deputy attorney general, Rod J. Rosenstein, had recommended he be dismissed. But Mr. Trump quickly undercut that argument, telling NBC News that he had been thinking about the Russia investigation when he fired Mr. Comey.
Asked why he was fired, Mr. Comey replied: “I take the president at his word — that I was fired because of the Russia investigation. Something about the way I was conducting it, the president felt, created pressure on him that he wanted to relieve.”
Mr. Comey questioned why Mr. Sessions had been involved in the discussions about his firing, given that Mr. Sessions had recused himself from the Russia case after his undisclosed contacts with the Russian ambassador to the United States were revealed. “If, as the president said, I was fired because of the Russia investigation, why was the attorney general involved in that chain?” Mr. Comey asked. “I don’t know.”
The Justice Department said Thursday that Mr. Sessions had been involved because the firing was related to concerns about Mr. Comey’s leadership and had nothing to do with any inquiry.
Mr. Comey also described his disappointment when the president asked that they be left alone after a meeting in the Oval Office with national security officials. Mr. Sessions stayed behind at first, but then left. “My sense was the attorney general knew he shouldn’t be leaving, which is why he was lingering,” Mr. Comey said. He testified that he later told Mr. Sessions to never again leave him alone with Mr. Trump.
Mr. Kasowitz said Mr. Trump had never sought a loyalty pledge, as Mr. Comey told the Senate. And he portrayed Mr. Comey as part of a stealth campaign to undermine Mr. Trump. “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.”
Mr. Comey’s memo was not classified, and the White House did not assert executive privilege over his conversations with Mr. Trump.
Though Mr. Comey told Mr. Trump three times that he was not under investigation, he said others at the F.B.I. had argued against offering that assurance. Because the F.B.I. was investigating possible coordination between the Trump campaign and Russia, one official argued, Mr. Trump’s activity would necessarily be scrutinized. Nevertheless, Mr. Comey said, “I thought it was fair to say what was literally true: There is not a counterintelligence investigation of Mr. Trump.”
But Mr. Comey said he had distrusted Mr. Trump from the first time they met, at Trump Tower before Inauguration Day. Mr. Comey ended the day in an F.B.I. vehicle, taking detailed notes about his conversations. “I was honestly concerned that he might lie about the nature of our meeting,” he said, “and so I thought it really important to document.”
Then, in February, when Mr. Trump cleared the Oval Office to talk about Mr. Flynn, Mr. Comey described an ominous feeling. “My impression was, something big is about to happen,” he said. “I need to remember every single word that is spoken.”