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

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.