Comey's testimony will be his first public comments since Trump fired him early last month, and he is likely to be asked about any conversations the president may have had with him about the ongoing investigation into Russian interference in the 2016 election.
Comey reportedly wrote memos describing conversations with Trump before he was fired in which Trump allegedly asked him to “let this go,” referring to the FBI's investigation of Trump's former national security adviser Michael Flynn.
Earlier, the White House had said that Trump was considering the use of executive privilege to halt Comey's testimony, essentially arguing that he is afforded an expectation of privacy in conversations he may have had with a government official.
But experts have said any attempt to assert executive privilege over Comey’s expected testimony would be on shaky ground legally, largely because he is no longer a government employee.
Trump also spoke publicly about his reasons for firing the FBI director and about his conversations with Comey. He has said Comey assured him he was not personally under investigation, and in an interview with NBC's Lester Holt, Trump criticized Comey as an attention seeker.
“He's a showboat, he's grandstander, the FBI has been in turmoil,” Trump said. “Regardless of recommendation, I was going to fire Comey knowing there was no good time to do it.”
While White House officials said in the days after Comey's dismissal that it was largely the result of a memo written by Deputy Attorney General Rod J. Rosenstein criticizing the FBI director's handling of the investigation into Hillary Clinton’s use of a private email server when she was secretary of state, Trump suggested in the NBC interview that the Russian investigation played a role in his decision.
“And in fact, when I decided to just do it, I said to myself — I said, you know, this Russia thing with Trump and Russia is a made-up story,” Trump continued. “It's an excuse by the Democrats for having lost an election that they should've won.”
Comey is set to testify before the Senate Intelligence Committee on Thursday in a hearing that will likely shed light on his conversations and interactions with Trump.
The Justice Department investigation into Russian interference in the election and any possible collusion with Trump campaign associates has now been taken over by a special counsel, former FBI director Robert Mueller.