Comey's testimony, based largely on written records he made after one-on-one conversations with Trump from January to April, casts light on Trump's behavior with the former FBI chief and the president's possible motives for firing Comey.
The ex-FBI director said he kept records of his meetings with Trump because he thought the president might lie.
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Last month, Trump tweeted a suggestion that he had recorded their conversations, saying Comey "better hope that there are no 'tapes'" of the talks.
@realDonaldTrump: James Comey better hope that there are no "tapes" of our conversations before he starts leaking to the press!
Comey told the Senate Intelligence Committee that he hopes his conversations with the president were recorded.
"I've seen the tweet about tapes. Lordy, I hope there are tapes," Comey said.
If there were, Comey said he thought there might be something that corroborated his account of events.
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In a detailed opening statement posted by the Senate Intelligence Committee on Wednesday, the ousted FBI director said that he understood Trump to be asking him to "drop" the probe into former national security advisor Michael Flynn when they spoke in February.
Trump abruptly fired Comey last month amid an FBI probe into Russian interference in the 2016 election and possible ties between the Trump campaign and the Kremlin.
While he understood he "could be fired by a president for any reason or no reason at all," Comey said he was confused and concerned by the White House's shifting explanations of his firing.
The former FBI chief said he was confused because Trump had told him that he hoped he would stay on the job. Comey started a 10-year term in 2013.
Comey said that the White House "chose to defame" him and alleged that the FBI was in "disarray."
"Those were lies, plain and simple," Comey told the Senate Intelligence Committee.
Comey said in his statement that he interpreted the president's comment as a request that the FBI "drop any investigation of Flynn in connection with false statements about his conversations with the Russian ambassador in December."
"I did not say I would 'let this go," Comey recounted in his written testimony.
However, the former FBI chief "did not understand the president to be talking about the broader investigation into Russia or possible links to his campaign."