Trump, a ratings-obsessed former reality television star, may not appreciate the worldwide attention paid to Comey's public testimony.
Trump, a ratings-obsessed former reality television star, may not appreciate the worldwide attention paid to Comey's public testimony, which is being touted as the Super Bowl of high political drama.
Comey is the star witness in the Senate Intelligence Committee's investigation of alleged Russian election meddling last year, with the possible collusion of the Trump campaign. The allegations have drawn comparison to the 1970s Watergate scandal that brought down president Richard Nixon.
Comey was given the go-ahead to deliver potentially explosive testimony after the White House announced it would not use its executive privilege to block his appearance, less than a month after he was controversially sacked by the president.
The former Federal Bureau of Investigation director is expected to dispute Trump's claim that Comey told him multiple times that he was not under investigation by the FBI, CNN reported sources familiar with Comey's thinking as saying.
Trump himself weighed in Tuesday, even as the revelations could spell more bad news for his troubled administration.
"I wish him luck," Trump said, when asked in a meeting with Republican leaders whether he had a message for the former FBI chief.
With Capitol Hill abuzz, at least two Washington bars were set to open their doors before the hearing's 10:00 am (1400 GMT) start to Washingtonians wanting to tune in live.
"Don't you like the suspense?" Senate Republican Marco Rubio, who is on the intelligence panel, asked a scrum of reporters.
"Rather than relying on articles and third-hand information, we're going to ask the director, and the American people are going to get to watch it."
The Senate's top Democrat, Chuck Schumer, offered a more somber assessment of Comey's testimony, which marks a moment of peril for the embattled president.
"I just hope he tells everything he can," Schumer said. "The American people, on a subject as serious as this, are entitled to the whole truth and nothing but."
A warm-up act of sorts comes Wednesday, when the same committee hears from Director of National Intelligence Dan Coats, National Security Agency (NSA) head Mike Rogers, interim FBI director Andrew McCabe, and Deputy US Attorney General Rod Rosenstein.
Adding to the drama, a top-secret NSA report leaked to online news outlet The Intercept shows that hackers from Russian military intelligence repeatedly tried to break into US voting systems before last year's presidential election.
Keen to crack down on leaks, the Trump administration quickly announced the arrest of a 25-year-old intelligence contractor on charges of violating the espionage act.
Comey's testimony will be his first public remarks since Trump summarily fired him on May 9.
The dismissal -- a stunning move by any measure -- came as the FBI is probing possible collusion between his campaign team and Russia, which US intelligence agencies concluded sought to tilt the election in the Republican's favor.
Comey is said to have written detailed notes about three conversations he had with Trump, which reportedly document the president's efforts to get the FBI to ease the investigation's focus on former national security advisor Michael Flynn.
Any confirmation that Trump tried to press Comey would open the president to damaging allegations that he attempted to obstruct an ongoing FBI investigation -- which several Democrats have warned would propel the crisis into Watergate-like territory.
Trump himself invoked Nixonian symbolism last month, when he warned via Twitter that Comey "better hope that there are no 'tapes' of our conversations."
Revelations that Nixon secretly taped visits in the White House, and refused to turn over the audio tapes under subpoena, led to his resignation in 1974.
Senator Mark Warner, the intelligence panel's top Democrat, said Trump would have violated longstanding guidelines if he pressured Comey to drop or slow-walk an investigation.
"It would be unthinkable if the president actually did what was reported," Warner told CBS News Sunday.
"We have no smoking gun at this point, but there is a lot of smoke."
What Comey will reveal, if anything, is the topic of intense speculation.
Republican committee member Senator Roy Blunt said he welcomed Comey's testimony, but warned there could be "a big problem" if the ousted FBI boss is too restrictive in his responses.
"I expect us to ask him questions to be sure that we get all of the answers we need, not just the answers he wants to give," he said.
The White House had suggested Trump could invoke executive privilege to protect the confidentiality of presidential discussions, but some aides were wary that may appear like a cover-up.
Trump's decision to fire Comey led the Justice Department to appoint a special counsel, ex-FBI director Robert Mueller, to investigate allegations of collusion.
He reportedly has met with Comey to discuss the probe, and Comey reportedly sought his approval to testify.