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

Senators on both sides of the aisle seemed surprised by House impeachment managers' move to call for witnesses Saturday, according to pool reporters inside the chamber.

Sen. Ron Johnson, R-Wis., turned to Sen. Mitt Romney, R-Utah., at one point and was visibly upset with him, even pointing at him once. The two went back and forth with Sen. Dan Sullivan, R-Alaska, in the middle of them.

Johnson said, "We should've just ended this, that's all I'm saying," and told Romney, "Blame you."

Romney was the only Republican to vote to convict Trump at his last impeachment trial.

When lead House impeachment manager Rep. Jamie Raskin, D-Md., raised bringing in Rep. Jamie Hererra Beutler, D-Wash., as a witness, Sen. Lindsey Graham, R-S.C., shook his head no and put his head down on his hand on his forehead.

Graham later joined four Republicans --Sens. Mitt Romney, Susan Collins, Lisa Murkowski and Ben Sasse -- in voting to hear witnesses after threatening to delay the trial with witnesses of his own.

Sources close to Trump are floored by the unexpected, 11th-hour motion to call witnesses in the impeachment trial of the former president.

"Stunned," "stupefied," and "digesting this” were responses provided by sources to ABC News. There is total panic in the air as the question looms of who may get called as a witness and who may step up to help Trump's defense team. 

The development to call witnesses revolves around the timeline of Trump's response to the attack on Jan. 6 and when he knew then-Vice President Mike Pence was in danger.

David Schoen, one of Trump's impeachment lawyers, threatened to quit Thursday night -- just hours before he was to mount a defense of Trump's actions.

It wasn't until Trump called Schoen directly that he agreed to remain on the team. It also led to the speaking roles and order of the attorneys during the Friday defense presentation being altered, according to the sources.

ABC News' Katherine Faulders and John Santucci 

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