"My impression is something big is about to happen. I need to remember every word that is spoken," he said of the numerous memos he wrote immediately after his encounters with the president.
"Shifting explanations" for Comey's firing
The former FBI director also harshly pushed back on Trump's changing explanations for why he had been let go, saying he was "confused" and "increasingly concerned" about the "shifting explanations" Trump gave. The president initially pointed to Comey's handling of the Hillary Clinton email investigation as the impetus, but later conceded it was because of his handling of the Russia investigation and claimed Comey was overseeing a demoralized FBI in disarray.
"So it confused me when I saw on television the president saying he actually fired me because of the Russia investigation and learned again from the media that he was telling, privately, other parties that my firing had relieved 'great pressure' on the Russia investigation," Comey said, referring to reporting on Trump's conversation with Russian officials in the Oval Office the day after the dismissal.
"The administration then chose to defame me, and more importantly the FBI," Comey said, by claiming the agency was "poorly led."
"Those were lies, plain and simple," Comey bluntly told the committee.
White House Deputy Press Secretary Sarah Sanders later pushed back on Comey's assertions, telling reporters that "I can definitely say the president is not a liar and I think it's frankly insulting" that the question was asked.
Awkward "loyalty" dinners and Oval Office pressure
Comey's highly anticipated testimony followed the release by the committee of his written statement on Wednesday, which ticked off in rich detail the extent to which Trump pressed him about the Russia investigation. Comey wrote that Trump did ask him for a "loyalty" pledge during a one-on-one dinner and later told Comey in a solo Oval Office meeting that he " hope[d] you can let ... go" of the Flynn investigation.
The president has denied both those accusations. But Comey's testimony so far has only confirmed the many bombshell reports over the past few weeks about the private conversations he had with Trump, many of them unprecedented and possibly inappropriate.
Comey told the committee that he did see Trump's request for loyalty from him -- an independent arbiter atop the FBI -- as a sort of quid pro quo.
"My common sense told me what's going on here is he's looking to get something in exchange for granting my request to stay in the job," Comey said.
He also said that in a now-infamous photo just days after Trump's inauguration in which the president shook his hand and embraced him, Trump whispered in his ear, "'I really look forward to working with you.'"
On Trump's Feb. 14 private conversation with Comey in the Oval Office — the day after Flynn was asked to resign for misleading Vice President Mike Pence over his conversations with the Russian ambassador during the transition — Comey said that he believed the president was indeed directing him to scuttle the investigation into Flynn.
"I took it as a direction," which he didn't follow, Comey said. "I took it as, this is what he wants me to do." Comey also added that, at that time, Flynn was indeed in "legal jeopardy" over his ties and contacts with the Russians.
He noted that Attorney General Jeff Sessions tried to linger in on that meeting, and he said that it was his "sense" that Sessions "knew he shouldn't be leaving." According to Comey's written testimony, he later told Sessions he didn't want to be left alone with Trump again. Comey said during questioning that he was "stunned" by that conversation and the president asking everyone else to leave, and later said it was a "significant fact" to him as a prosecutor that Trump wanted to speak with him alone.
Comey did testify that he didn't believe Trump was asking Comey to stop the broader Russia investigation being conducted by the FBI, but that while his conversation with Trump was "disturbing," he didn't "think it's for me to say that the conversation I had with the president was an effort to obstruct."
Obstruction of justice? Up to special counsel Mueller to "sort that out"
Later asked by Sen. Joe Manchin, D-W.Va., whether Trump's interactions with him over Flynn rose to the level of obstruction of justice, Comey responded that was newly appointed special counsel Robert Mueller's "job to sort that out."
Comey said he had indeed seen Trump's tweet last month suggesting that the president had "tapes" of their conversations — and that if those did exist, they would corroborate his testimony.
"Lordy, I hope there are tapes," he told senators.
And, Comey revealed that it was Trump's tweet about those alleged "tapes" that prompted him to call up a friend to leak the memos about his conversations with the president to the press last month in hopes it would lead to the appointment of a special counsel to oversee the Russia investigation.
Republicans have already seized on one section of Comey's written testimony as vindication. The former FBI director does detail in his written submission to the committee how he told Trump on three separate occasions that he himself was not under investigation -- a surprising assertion Trump put in his termination letter to Comey.
Comey told the committee that deliberations with senior FBI leadership about whether to tell the president he was not personally under investigation, beginning in January before he was inaugurated, were not unanimous.
"One of the members of the leadership team had a view that although it was technically true, we did not have a counterintelligence file case open on then-President-elect Trump, his concern was that because we're looking at the potential -- again that's the subject of the investigation -- coordination between the campaign and Russia, because it was President Trump -- President-elect Trump's campaign, this person's view was inevitably his behavior, his conduct will fall within the scope of that work. And so he was reluctant to make the statement that I made. I disagreed," Comey said. "I thought it was fair to say what was literally true — there is not a counterintelligence investigation of Mr. Trump -- and I decided in the moment to say it given the nature of our conversation."
He later confirmed that when he was let go on May 9, there was no counterintelligence, nor criminal investigation, of Trump individually, and that the president was not personally under investigation.
Asked by Sen. Tom Cotton, R-Ark., as to whether he believed Trump colluded with Russia during the campaign, Comey responded, "I don't think I should answer in an open setting." Following his open hearing with members of the Intelligence Committee, Comey did go into a closed briefing with senators.
Comey was also pressed by Republicans on the committee, including Florida Sen. Marco Rubio, on why he didn't alert White House officials or the White House Counsel's Office about what he believed were inappropriate conversations with Trump and a breach of protocol.
"I don't know," Comey responded to Rubio. "I think the circumstances were such that I was a bit stunned and didn't have the presence of mind."
Comey critical of Obama Attorney General Loretta Lynch
Republicans also pressed Comey on how he handled the investigation into Hillary Clinton's emails during the 2016 campaign, usurping then-Attorney General Loretta Lynch by announcing the FBI was not recommending prosecution for handling of classified information on Clinton's private server.
Comey testified he was disturbed by Lynch's tarmac meeting with Clinton's husband, former President Bill Clinton, and that was one reason he made his announcement in July, though he did say at that time he believed Hillary Clinton had been careless with classified information.
"I didn't believe she could credibly decline that investigation, at least not without grievous damage to the Department of Justice and the FBI," Comey said of Obama's attorney general.
Comey said it made him uncomfortable that Lynch had directed him to refer to the Clinton email investigation as a "matter" and not an investigation, even though she was, indeed, under criminal investigation.
Pressed by Sen. John McCain, R-Ariz., as to why he didn't call for an independent counsel to handle that matter, Comey said that he "knew there was no case there" and that "calling for a special counsel would be brutally unfair."
Republicans push back that Trump has been "vindicated"
The president himself has not yet directly responded to Comey's testimony, and has not tweeted, as many people speculated he might. However, the president's son, Donald Trump Jr., did largely live-tweet the event.