Republicans are scrambling to prevent a protracted, messy fight as they try to dismiss renewed talk of calling witnesses during President Trump's impeachment trial.

Opening the door to witnesses would set up a two-phased headache for GOP leadership: first, in the form of a free-for-all on the Senate floor with conservatives vowing to subpoena figures like former Vice President Joe Biden, his son Hunter Biden and the anonymous whistleblower; and second, with a lengthy court battle that would drag out the duration of the trial.

Senate Republicans emerged from a closed-door caucus meeting Tuesday voicing renewed confidence they will avoid a fight over witnesses, but tensions were high following this week's news that former national security adviser John Bolton claimed in a forthcoming book that Trump tied Ukraine aid to the country helping with investigations into Democrats. The bombshell report rattled the caucus, where Senate Majority Leader Mitch McConnell (R-Ky.) is trying to navigate his slim 53-47 majority.

GOP senators said there were "no deals," or significant decisions made during Tuesday's meeting, and leadership does not yet have a lock on the 51 votes to block witnesses. But some, including Sen. John Barrasso (R-Wyo.), argued it was time to move on, while stressing discussions would continue.

"The consensus is that we've heard enough and it's time to go to a final judgement," Barrasso said.

Under a rules resolution passed last week, the Senate will hold a vote on whether additional witnesses or documents will be allowed in the trial. That vote is expected Friday.

Republicans are warning their GOP colleagues that if they open the door to witnesses, they could set up an unpredictable floor fight that would put a spotlight on party divisions.

Sen. John Thune (R-S.D.) questioned who, if anyone, would benefit by such a fight, where there would be few restrictions on who could try to be called as a witness.

"Presumably, if the Democrats want to call witnesses, our guys are going to want to call the Bidens and the whistleblower. You get into that kind of argument and that could be - I'm not sure in the end that serves anybody's interest well," Thune said.

Barrasso, meanwhile, warned that allowing witnesses could turn the Senate into a "circus."

Democrats would need four Republicans to cross the aisle on the initial vote on whether to call witnesses, and then four again on any request for Bolton or other administration officials.

Sen. Mitt Romney (R-Utah) has publicly and privately made the case for wanting to hear from Bolton, though he's stopped short of saying he will vote for witnesses.

Sen. Lisa Murkowski (R-Alaska) has said she is "curious" to know what Bolton has to say. Sen. Susan Collins (R-Maine) said in a CBS News interview that aired Tuesday that she is "very likely" to support calling witnesses.

"I, for one, believe that there's some gaps, some ambiguities that need to be cleared up," Collins said.

Both Collins and Murkowski have said they will wait until after opening arguments and senators' floor questions to make a final decision on whether they will vote to call witnesses. Trump's team wrapped their defense on Tuesday and senators are expected to start asking questions Wednesday.

As an effort to pressure their GOP colleagues into opposing witnesses, conservatives and Trump allies are warning that a witness fight could turn unpredictable.

Sen. Josh Hawley (R-Mo.) is planning to force votes on calling the Bidens and House Intelligence Committee Chairman Adam Schiff (D-Calif.) if his GOP colleagues side with Democrats and allow witnesses.

"If we call witnesses, if my colleagues and others decide, 'You know what, we've got to have witnesses,' then let's call everybody who's going to be relevant. This isn't just about John Bolton, this should be about the whistleblower, Adam Schiff, Hunter Biden. Let's hear from them all," Hawley told Fox News.

Sen. Rand Paul (R-Ky.) characterized himself as for "all witnesses or no witnesses," but questioned why his GOP colleagues would trust Bolton enough to subpoena him and drag out the trial.

"You know, I think we've heard a lot of witnesses and we've heard a lot of testimony, and I think we're at the point where we've heard enough, frankly," he said. "I think at this point if you want to hear from John Bolton, you have to ask yourself is he a disinterested party. ... Or is he someone who is very unhappy, disgruntled, fired employee who now has a motive."

Sen. Kevin Cramer (R-N.D.) said the fact that calling Bolton could lead to a laundry list of other witnesses was a reason why no witnesses should be called.

"If we open the door of witness, I think Adam Schiff, he's a fact witness, and the whistleblower certainly is," Cramer said.

He added that House managers meanwhile would want to use the witnesses to go "fishing."

In addition to a nasty floor fight, Republicans are warning about a weeks- or even months-long legal fight that would effectively put the Senate trial in limbo.

Trump has signaled he would invoke executive privilege if Bolton is called to testify, which would prompt an automatic court battle.

Members of GOP leadership said the threat of a court fight is affecting the thinking of the caucus amid the internal debate over whether to call Bolton and potentially others.

"I think people are concerned that every day we spend on an impeachment is a day we're not spending doing other work for the American public," Barrasso said when asked how Republicans were thinking about a potential legal fight.

Thune suggested there are some GOP senators who could be open to calling witnesses, but had concerns about the executive privilege fight and a prolonged trial.

"I think there's been some fluidity in people who are, who have entertained the possibility but also have a lot of questions about what that looks like," Thune said. "Will this thing drag out? Will we get both sides arguing over witnesses for the next five weeks, litigating privilege?"