“I’d like to hear what he has to say. He’s got firsthand information; I think that would be helpful,” Romney said Monday.

But the Utah senator, a frequent Trump critic, stopped short of saying he would support a motion to subpoena Bolton during the trial.

“What the process is to make that happen, I don’t have an answer for you,” Romney said.

Bolton’s surprise offer to speak scrambled the political calculus surrounding the impeachment trial on Capitol Hill, where Democrats and Republicans have been unable to reach an agreement on witness testimony and other rules before the proceedings begin. House Speaker Nancy Pelosi (D-Calif.) has so far refused to send the articles of impeachment to the Senate, meaning Senate Majority Leader Mitch McConnell (R-Ky.) has not been able to start the trial.

Democrats are hoping Bolton’s willingness to come forward with what his lawyer claims is new information about Trump’s pressure campaign on Ukraine will encourage moderate Republicans to consider expanding the scope and length of the Senate trial.

But other than Romney, no other GOP senators welcomed Bolton’s testimony on Monday.

Sen. Susan Collins (R-Maine), who is up for reelection next year, reiterated that a decision on witness testimony ought to come after the trial begins and presentation of evidence has been made ― as was the case during the 1999 impeachment trial of President Bill Clinton.

“I can’t say at this point who the specific witnesses should be, if any,” Collins told HuffPost on Monday when asked about Bolton’s offer to testify, though she previously said in an interview that she is “open” to calling witnesses in the trial.

Sen. Lisa Murkowski (R-Alaska), another moderate, agreed.

“We’ve got to get to the first place first, which is starting [the trial],” she told reporters.

Their stance on the parameters of the impeachment trial aligns them with McConnell, who has all but promised a swift acquittal of Trump. McConnell is pushing for following the 1999 framework and did not respond to a question about Bolton’s offer to testify on Monday.

Sen. Cory Gardner (R-Colo.), another vulnerable Republican up for reelection next year, did not say whether he planned to support a motion to subpoena Bolton.

“I know you guys want to have a trial by Twitter, but until she has the articles sent over, there is no trial,” he said, referring to Pelosi.

Sen. John Cornyn (R-Texas) did not rule out voting to subpoena Bolton, but he, too, said the question of witnesses should be left for later in the trial.

“If 51 senators want to hear from Ambassador Bolton, I think that’s fine. It doesn’t have to be live, it could be a deposition,” Cornyn said, adding that Bolton’s testimony may even help the president’s case against impeachment.

Other Republicans said they had no interest in hearing about evidence not already presented by the House impeachment investigators. Sen. Todd Young (R-Ind.)., for example, argued it would set a “bad precedent” if the Senate “made it a common practice to improve upon defective articles of impeachment” by inviting new testimony.

Three witnesses were subpoenaed during the Clinton trial in 1999, though senators viewed their depositions behind closed doors on videotape.

House Democrats decided not to subpoena Bolton while the chamber mulled over whether to draft impeachment articles last year. They reached the decision after the White House declared it wouldn’t cooperate with the hearings and instructed top officials who’d already been subpoenaed not to comply.

Sen. John Kennedy (R-La.) suggested Bolton’s offer to testify may be moot, given the likelihood of the Trump administration trying to block it by asserting executive privilege.

“There’s still the issue of executive privilege,” he said. “I think the president’s lawyers are going to assert it ... I don’t see why everybody’s getting all lubed up about it.”

Asked if he was open to subpoenaing Bolton now that he expressed a willingness to speak, House Intelligence Committee Chairman Adam Schiff (D-Calif.) told reporters on Monday he wasn’t ruling it out.

“We’re not foreclosing anything, but he really should testify in a Senate trial. That makes the most sense,” Schiff said.