After rancorous arguments between the House impeachment managers and Mr. Trump‘s lawyers, senators voted 55-45 in favor of calling witnesses.
Five Republicans voted with all 50 Democrats: Sens. Susan Collins of Maine, Lindsey Graham of South Carolina, Lisa Murkowski of Alaska, Mitt Romney of Utah and Ben Sasse of Nebraska.
Mr. Graham changed his vote to “yes,” saying if the Democrats want witnesses, he envisions a lengthy delay with many witnesses called by Mr. Trump‘s side.
Most Republicans reacted angrily to the development, saying it would prolong the trial and exacerbate an already bitterly partisan drama.
“It’s just like opening up a wound and just rubbing salt in it,” said Sen. Ron Johnson, Wisconsin Republican. “Trump supporters understand that, and it just inflames the situation … rather than bring this to a close. We’re trying to put the fire out, and these guys [Democrats] are lighting the fire.”
The trial had been expected to move to a final vote on Saturday. But Rep. Jamie Raskin of Maryland, the lead House impeachment manager, opened the session by announcing that Democrats wanted to subpoena Republican Rep. Jaime Herrera Beutler of Washington state as a witness.
Ms. Herrera Beutler reiterated in a statement Friday night her claim about a phone call between Mr. Trump and House Minority Leader Kevin McCarthy, California Republican, as the rioters were attacking the Capitol on Jan. 6. Mr. McCarthy had called Mr. Trump at the White House urging him to call off the rioters.
“Well Kevin, I guess these people are more upset about the election than you are,” Mr. Trump allegedly told Mr. McCarthy, according to Ms. Herrera Beutler.
Mr. Raskin told senators, “Needless to say, this is an additional critical piece of corroborating evidence confirming the charges before you. We want to subpoena her. We would be prepared to proceed by Zoom deposition of an hour or less .. and then proceed to the next phase of the trial.”
Trump lawyer Michael van der Veen objected heatedly.
“If they want to have witnesses, I’m going to need at least over 100 depositions, not just one,” he told the Senate. “If you vote for witnesses, do not handcuff me. I’m going to slap subpoenas on a good number of people, if witnesses are what is required here.”
Mr. Trump‘s legal team pushed back on the comment attributed to the former president, saying Mr. McCarthy has disclaimed the rumor, and that the trial should conclude Saturday.
“This entire proceeding is based on rumor, report and innuendo,” said Mr. van der Veen. “We should close this case out today.”
He said if senators voted to allow witnesses, he would need to do a thorough investigation and conduct depositions at his law office in Philadelphia. The Democratic side of the chamber broke out in laughter.
“I don’t know why you’re laughing,” Mr. van der Veen said. “That’s civil process. That is the way we lawyers do it. I haven’t laughed at any of you. And there’s nothing laughable here.”
Sen. Patrick Leahy, Vermont Democrat who is overseeing the trial, called for order.
The next step was for Democrat and Republican senators to craft a resolution on how many witnesses will be called.
During a break in the trial, a visibly angry Mr. Johnson could be seen talking animatedly with Republican colleagues on the Senate floor.
“We should’ve just ended this, that’s all I’m saying,” Mr. Johnson told them.
Sen. Bill Cassidy, Louisiana Republican, relayed to reporters a comment from his colleague, Sen. Richard Shelby, Alabama Republican, about the 11th-hour twist on Saturday.
“Shelby says he’s seen three of these [impeachment trials], and this is the craziest,” Mr. Cassidy said.
Mr. Trump‘s lawyers had warned earlier that they might call House Speaker Nancy Pelosi as a witness, as the person ultimately responsible for Capitol security. Vice President Kamala D. Harris’s name also has been tossed around as a potential witness.
Ms. Herrera Beutler was one of ten House Republicans who voted for Mr. Trump‘s impeachment on Jan. 13. She urged anyone else with knowledge of the phone call between Mr. Trump and Mr. McCarthy to come forward.
“To the patriots who were standing next to the former president as these conversations were happening, or even to the former vice president: if you have something to add here, now would be the time,” she said in a statement.