Comey's testimony expected to shut down Capitol Hill Rep. Jackie Speier: "This will be watched as much as the Watergate hearings."

 -- It won't be business as usual on Capitol Hill tomorrow.

Former FBI Director James Comey's appearance before the Senate Intelligence Committee is expected to captivate lawmakers -- and grind some official business to a halt.

"This will be watched as much as the Watergate hearings," said Rep. Jackie Speier (D-Calif.), a member of the House Intelligence Committee, who plans to watch the hearing.

Several House members -– including Rep. Mike Quigley (D-Illinois), and the ubiquitous Rep. Sheila Jackson Lee (D-Texas) -- are taking the unusual step of crossing the Capitol on a busy legislative day to sit in on the Senate hearing.

Sens. Jack Reed (D-Rhode Island) and John McCain (R-Arizona), plan to take advantage of their privileges as former committee members: They will be sitting at the dais with the current members and will get to question Comey.

Even members leaving Washington are feeling the pull. Rep. Carolyn Maloney (D-N.Y.), who is slipping out of town to attend her daughter's graduation from MIT, told ABC News she is planning to sneak in some C-Span in Cambridge, Massachusetts.

Rep. Peter King (R-N.Y.) will watch the hearing Thursday, but he is worried about Trump retaliating on Twitter in real time.

"He can only hurt [his case]," King said in an interview. "He should just stay quiet."

King, who said Comey's statement released by the Senate Intelligence Committee today was "very positive" for the president -- because it appeared to back up his claim that Comey repeatedly told him he wasn't under investigation -- said Trump should leave any rebuttal to his lawyer.

"The danger is he responds to something inflammatory that some Democratic senator is going to ask, a leading question with a criminal implication ... and the president’s going to tweet quickly without checking all his records," he added.

Also on Thursday, House GOP leaders, forging ahead with their agenda, have scheduled a vote on the Financial CHOICE Act, a consequential proposal to roll back Dodd-Frank that Speaker Paul Ryan has called one of the "crown jewels" of the Republican agenda.

They have also cancelled votes planned for Friday, giving members an opportunity to leave Washington -- and questions from the Capitol Hill press corps about Comey's testimony -- a day early.