Trump's team is gearing up to undermine Comey in response to his Senate testimony
The Washington Post reported on Wednesday that Trump has spent the last several days "seething" about "fake news" while watching cable TV and tweeting without regard for his advisers' advice.
Major cable news networks have featured countdowns this week to Comey's live testimony, which will interrupt regular programming and is being called "Washington's Super Bowl."
The Post described Trump as "consumed, haunted and antagonized" by the FBI's investigation into possible collusion between his campaign aides and the Russian government and "spoiling for a fight" with Comey.
"He's infuriated at a deep-gut, personal level that the elite media has tolerated [the Russia story] and praised Comey," former House speaker Newt Gingrich told the Post. "He's not going to let some guy like that smear him without punching him as hard as he can."
Dozens of White House aides and others close to the president told the Post that Trump is being encouraged by his top lawyers and advisers to refrain from commenting on Comey's testimony on Twitter. But they fear the president will ignore their recommendations.
Washington Post reporter Robert Costa said sources told him that Trump might even live tweet the Comey hearing if he feels the need to respond to Comey's testimony.
They also expressed concern about the political and legal repercussions of Trump's unpredictable behavior, and expressed dismay that the president does not seem capable of focusing on his administration's policy agenda.
One Republican allied with the White House described aides' response to Trump's public reactions as: "Please, don't, you're not helping things."
Trump has blasted Comey on Twitter repeatedly since firing him.
In May, Trump tweeted: "James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press!"
Trump has also called investigations into whether his campaign colluded with Russians a "witch hunt."
The Associated Press reported on Wednesday that Trump's aides are crafting a response to Comey's testimony that will attempt to undermine him and deflect attention away from his allegations, which Comey detailed in a prepared statement released by the Senate on Wednesday afternoon.
Sources told the Post that Trump's team is planning portray Comey as a "showboat" - a term Trump has used to describe him. A set of relatively low-profile surrogates are prepared to appear on conservative media outlets on Thursday in an attempt to disseminate the White House's message.
And Trump's messaging is being supported by allied groups outside the White House.
"If we feel he crosses a line, we'll fire back," said Ed Rollins, the chief strategist at the conservative Great America PAC, told the AP.
Just the day before Comey's scheduled appearance, Trump announced his nominee for FBI Director, Christopher Wray, a former assistant attorney general under George W. Bush who served as New Jersey Gov. Chris Christie's personal attorney during the Bridgegate scandal.