The details shared by Comey are likely to further fuel the debate over whether the president may have attempted to obstruct justice by pressuring the FBI director about a sensitive investigation.
Comey wrote in his testimony that Trump told him that "I need loyalty, I expect loyalty" in a private White House dinner conversation in January.
"I didn't move, speak, or change my facial expression in any way during the awkward silence that followed," Comey wrote. "We simply looked at each other in silence. The conversation then moved on, but he returned to the subject near the end of our dinner."
Anticipation in Washington for the hearing is so high that several bars are opening early or offering specials for the event.
"Comey has made a career of providing bombshell testimony to Congress,'' said Tracy Schmaler, a former Senate Judiciary Committee staffer who attended a 2007 hearing in which Comey captivated the capital with an account of apparent White House interference with Justice Department decision-making. "In that respect, Thursday will be what everyone's expecting — the most anticipated hearing so far in the Trump administration."
Analysts who know and have studied Comey's career expect that he will tell the tale in a way that draws clear moral lines through what might otherwise be murky legal matters. "James Comey has the quiet confidence and a track record of knowing how to dominate, how to direct the story," said Karen Greenberg, the director of the Center on National Security at Fordham University.
Greenberg said she expects that he will "stand up for the integrity of the law in a way that the public can understand."
"He trusts his conscience and he's not afraid to stand up to people who he thinks are wrong," she said. "It's where he sees morality intersect with the law."
Comey's written testimony, released Wednesday, describes a strained, awkward relationship with Trump, punctuated by exchanges in which the president expressed his displeasure about the Russia probe in ways that alarmed the FBI director. Even the number of contacts between the two were alarming to Comey, who noted that he only spoke twice privately with President Barack Obama.
Senate Intelligence Committee Chairman Richard Burr (R-N.C.), who is leading the Senate investigation of possible Russian coordination with Trump associates, said he was not alarmed by Comey's written testimony.
"I don't think it's wrong to ask for loyalty of anyone inside an administration," Burr said. "I don't think of what I've read there's anything of wrongdoing."
Democratic lawmakers have repeatedly tried to learn more about any conversations between Trump and officials in which the president tries to gain help pushing back against the FBI's Russia investigation. On Wednesday, two of the country's top intelligence officials went before the Senate Intelligence Committee and refused to discuss the specifics of conversations with the president, frustrating severallawmakers. Based on the testimony already released, Comey will have no such hesitation on Thursday.