Senate Republicans are backing off initial, ironclad opposition to witnesses in the upcoming trial to adjudicate two articles of impeachment against President Trump.

As House Democrats approved charges of abuse of power and obstruction of Congress in mid-December, most Senate Republicans signaled they were inclined to conclude an impeachment trial without witness testimony immediately following arguments from the defense and prosecution. But having agreed this week to broad contours for trial procedure, Republicans are declining to rule out witnesses, saying it depends on what they hear from House prosecutors and the White House defense.

“That seems like a reasonable approach,” Sen. John Hoeven, a North Dakota Republican, said Thursday.

Sen. Rick Scott said he wants to get through arguments and question-and-answer phases of the trial before deciding on witnesses. “I’m going to get through the first part of it, figure out what they present, and figure it out then,” the Florida Republican said. “I think we ought to go through the normal process.”

Senate Majority Mitch McConnell of Kentucky and Senate Minority Leader Charles Schumer of New York failed to reach an agreement on trial procedure. But McConnell obtained from at least 51 of his 52 Republican colleagues commitments to support rules similar to those implemented for the 1999 impeachment trial of President Bill Clinton. Republicans are waiting for House Speaker Nancy Pelosi to transmit impeachment articles to the Senate before introducing a rules resolution for floor consideration.

In the Clinton trial, whether to call specific witnesses and in what format their testimony should be provided — depositions or live on the Senate floor — was addressed in a second resolution. That is how Senate Republicans are approaching this issue for the Trump trial.

Some Republicans are indicating that if GOP support for witnesses materializes, it might only be for additional testimony from people who testified in the House. That seems to be the most realistic possible outcome. Most Republicans firmly oppose exceeding the scope of the House investigation. Hearing testimony from new witnesses might be interpreted that way — especially by Trump and his loyal voting base.

“When we go back to the Clinton trial, the three witnesses that were called were all witnesses that had been previously called by the House,” said Sen. James Lankford, an Oklahoma Republican. “Now, that decision’s not made and can’t be made until you actually hear all the testimony and go through the process.”

At least one Republican is open to new witnesses, a key demand of Senate Democrats. Others might follow.

“I’d like to hear from John Bolton. We’ll see if there’s anybody else,” Sen. Mitt Romney of Utah said, referring to Trump’s former national security adviser who was in the middle of events that sparked an impeachment investigation into the president’s dealings with Ukraine. Bolton this week said he would comply with a Senate subpoena.

However, the likelihood of witnesses being called in the Senate is unclear at best, and at worst, slim. Hearing from any specific witness requires a vote of 51 senators. And some Republicans predict that any attempts to subpoena testimony will break down over partisan disagreements related to who should appear.

For instance, in addition to Bolton, Democrats want to hear from acting White House chief of staff Mick Mulvaney and top aides in the Office of Management and Budget, whom Trump previously blocked from testifying in the House. Some Republicans, meanwhile, would want to call Hunter Biden, the son of former Vice President Joe Biden; the government whistleblower who sparked the House investigation; and others.

“There would be a choice of witnesses on both sides,” Sen. Mike Braun, an Indiana Republican, said. “Schumer’s been able to control the dialogue that only he can get witnesses. And of course, that wouldn’t be the case.”

The other factor working against witnesses is some Republicans’ continued opposition to hearing fresh testimony and extending the process longer than necessary. More than three-quarters of 53 Senate Republicans are poised to acquit Trump. They have been critical of the process in the House that led to Trump’s impeachment while arguing that the president’s actions, however questionable, did not warrant the rebuke.

Pelosi’s decision to sit on the articles, in what amounted to a failed bid to pressure Senate Republicans to approve the Democrats’ list of witnesses upfront, only hardened GOP resolve.

“I think it’s a flimsy case,” said John Barrasso of Wyoming, the No. 3 ranking Senate Republican. “I want to hear what [Democrats] have to say, then I want to hear the defense from the president, and I’m likely ready to vote on the final outcome at that point.”