Sen.(R-Iowa), asked about the potential of a one-for-one deal and the discussion within the GOP lunch, argued that witnesses wouldn't "change the facts in this case."

"But there didn't seem to be much support for it," he added. "Not at this point."

Sen.(R-S.D.) asked about talk during the GOP lunch about a one-for-one deal, acknowledged that it was "discussed."

But GOP senators signaled that the idea of a swap didn't currently have much support within the caucus, nor does it have the blessing of Senate Majority Leader(R-Ky.).

The New York Times reported on Sunday night that Bolton, in his book, claims that Trump linked $391 million in Ukraine aid to the country helping with investigations into Democrats, including former Vice President Biden and his son Hunter Biden.

The re-emergence of the idea, broached by Sen.(R-Pa.) during the lunch, comes after former national security adviser has upended the impeachment trial with his forthcoming memoir.

Republican senators discussed the idea of an impeachment witness swap, where they could call a witness for House managers in return for the same number for, during a closed-door caucus meeting on Monday.

Sen.(R-N.D.) added that didn't "see the need for more witnesses."

Under the theory, spearheaded by Cruz, if four GOP senators side with Democrats and subpoena Bolton, Republicans should also call someone off of Trump's witness wishlist, like Hunter Biden.

"Ted and I have been talking about reciprocity on witnesses. ...I don't think Pat originated it," said Sen. Mike Braun (R-Ind.), asked about the idea of a swap. "He just, I guess, would be comfortable with it."

Asked about McConnell's input on the idea of a witness swap, Braun noted the idea was coming from other senators, like Cruz, and not the GOP leader.

"He has not talked at all about witnesses," Braun said.

The GOP leader has said publicly and privately that he wants to wrap the trial without witnesses. Opening the door to witnesses, McConnell and top allies have warned, could drag out the impeachment trial for weeks, if not months.

Rounds added that "several different options" were thrown out during lunch about which witnesses would be included in the potential trade off.

If Republicans are going to pull off the witness swap, they would have to go it alone and put up the 51 votes to call a Trump-preferred witness from their own 53-member caucus.

"I would agree strongly against becoming co-conspirators with the Trump administration," Murphy told reporters.

The message from McConnell to Republicans during the closed-door lunch was to keep their powder dry on the question of witnesses until they get closer to Friday's vote.

"I just think it's too early to say," he said asked about GOP support for witnesses. "I would describe it as ... fairly fluid."