Trump impeachment trial live updates: Biden says charge 'not in dispute' in 1st comments on acquittal

Republican Sen. Lindsey Graham, who changed his vote to allow witnesses in the impeachment trial of Trump, has threatened to summon all kinds of witnesses if Democrats moved forward with calling for them.

Before the trial began Saturday, Graham tweeted, "If you want a delay, it will be a long one with many, many witnesses."

It's a sentiment shared by Trump's defense attorney Michael van der Veen who said he’ll subpoena hundreds -- including House Speaker Nancy Pelosi and Vice President Kamala Harris.

"The only thing that I ask, if you vote for witnesses, do not handcuff me by limiting the number of witnesses that I can have," he said before the senators voted 55-45 to allow them.

Senators, at one point, laughed at van der Veen, a personal injury attorney based in Philadelphia, for saying he wanted everyone deposed in his office there.

"None of these depositions should be done by Zoom. We didn't do this hearing by Zoom. These depositions should be done in person, in my office, in Philadelphia," he said, to laughter. "I haven't laughed at any of you and there's nothing laughable here."

After five GOP senators joined Democrats in voting for witnesses, leadership from both sides now need to figure out what the next steps of this trial will be. A quorum was called while each side confers among themselves.

Both legal teams left the Senate chamber.

-ABC News' Trish Turner

In an 11th-hour development, the Senate has moved to call witnesses in Trump's second impeachment trial. Witnesses were not allowed at his first trial.

Five Republican senators joined Democrats on the vote Saturday brining it to 55-45.

Republican Sen. Lindsey Graham, a close ally of the former president, changed his vote after the call was read back to support witnesses, joining Republican Sens. Mitt Romney, Susan Collins, Lisa Murkowski and Ben Sasse.

The Senate moved to allow witnesses after Lead House impeachment manager Rep. Jamie Raskin, D-Md., called to subpoena Rep. Jaime Herrera Beutler, R-Wash., after she tweeted out a statement overnight reiterating details surrounding House Minority Leader Kevin McCarthy's call with Trump during the Capitol siege.

Trump's defense team slammed the notion.

In a blistering statement to reporters before the impeachment trial began on Saturday morning, Sen. Sherrod Brown, D-Ohio, called his GOP colleagues "spineless" for being poised to vote not to convict Trump out of fear he will campaign against them.

"It's so clear this president abused his power," Brown said. "It's so clear he incited violence. And my colleagues just refuse to see it because of their abject fear of Donald Trump."

"I've watched my spineless colleagues walk around with fear in their eyes for four years," Brown later continued. "And so maybe I shouldn't be surprised."

-ABC News' Benjamin Siegel