The White House’s plans for a speedy impeachment trial were thrown into doubt Tuesday with Senate Republicans floating competing proposals on how to deal with new explosive revelations from ex-national security adviser John Bolton -- and Senate Majority Leader Mitch McConnell telling Republicans he doesn’t yet have enough votes to block the calling of impeachment witnesses.

GOP senators were all over the map on Tuesday as President Trump’s defense team called Bolton’s manuscript “inadmissible” and warned against opening the door to new wild-card information in the ongoing trial. Democrats have repeatedly called for Bolton to testify.

A source with knowledge of McConnell’s comments confirmed to Fox Business that the Kentucky Republican told people in a private meeting Tuesday that the GOP did not have the votes to block impeachment witnesses. A second source stressed that McConnell said he didn’t yet have the votes, with other sources saying Senate GOP leadership didn’t think the fight was over, and conversations were ongoing. The Wall Street Journal first reported McConnell’s comments.

Later Tuesday night, a Senate leadership source told Fox News that Republicans were assessing the viability of two alternative options, in the event there is majority support for additional witnesses. "Plan B," the source said, is to amend any resolution calling for a particular witness to also include a package of witnesses that wouldn't win enough support of the Senate. For example, if the Democrats seek to call Bolton, Republicans might seek to question Hunter Biden or Rep. Adam Schiff, D-Calif., over his panel's contacts with the whistleblower.

That proposal could afford moderate Republicans the political cover of voting in favor of witnesses, while ultimately rejecting a witness package.

Additonally, the White House retains the option to exert executive privilege to block witnesses, including Bolton, the source emphasized. That might end up in a court battle, and could prove dicey if Bolton opts to defy the White House's assertion of privilege.

Meanwhile, Sen. James Lankford, R-Okla., called for Bolton’s unpublished manuscript to be made available for senators to read in a classified Sensitive Compartmented Information Facility (SCIF) to understand what Bolton was alleging. His proposal got an ally in influential Sen. Lindsey Graham, R-S.C., who called the idea a “reasonable solution.”

TRUMP LAWYER CALLS BOLTON BOOK 'INADMISSIBLE,' AS DEFENSE TEAM WRAPS IMPEACHMENT ARGUMENTS

Some senators suggested that Bolton just spill the beans in a news conference on the sidelines of the impeachment trial.

“The Wall Street Journal has called for John to just come forward -- just tell the public what you know,” Sen. Ron Johnson, R-Wis., said. “I think that actually [would] be a smart thing. I’d encourage John to do that without involving the trial.”

The creative suggestions came after The New York Times reported Bolton’s manuscript included a claim that Trump explicitly linked a hold on military aid to Ukraine to an investigation into Joe and Hunter Biden. Trump told Bolton in August, according to a transcript of Bolton’s forthcoming book reviewed by The Times, “that he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats, including the Bidens.”

The stunning leak -- which Johnson called “suspicious” -- has allowed House impeachment managers to ramp up their calls for Bolton to testify. The Democrats warned that if Senate Republicans quashed witnesses, they’d engage in a “cover-up,” especially since they said the book eventually would come out.

That left some Republicans searching for an off-ramp that would allow Bolton’s allegations to air out while not derailing the entire Senate impeachment trial. A Bolton news conference or a manuscript reading seemed like two potential middle grounds floated Tuesday.

BOLTON FOR BIDEN? WITNESS SWAP TALK REVIVED IN WAKE OF BOMBSHELL BOOK MANUSCRIPT

Other senators, including Pat Toomey, R-Pa., re-upped the idea of witness reciprocity as a way to hear from Bolton but also gain testimony from Hunter Biden or Joe Biden in return. But, Democrats have repeatedly shut down making any deals with the GOP for any of the Bidens, saying the father and son were just a distraction from charges against the president.

Other battle lines seemed to harden. On one end, the calls for witnesses -- led by Sen. Mitt Romney of Utah -- only got stronger. Meanwhile, Trump loyalists were quick to shut down the talk of prolonging the trial a minute longer than necessary.

Sen. John Cornyn, R-Texas, said he’s not in favor of subpoenaing the Bolton manuscript: “I think we know all we need to know," he said.

Sen. Rand Paul, R-Ky., on Tuesday suggested that Bolton was a disgruntled fired employee with the motive of money.

“The Democrats have spent a lot of time imagining what the president’s motives are,” Paul said. “Someone ought to spend some time imagining what John Bolton’s motives are other than making millions of dollars to trash the president.”

Sen. Kevin Cramer, R-N.D., said opening the door on even the manuscript could lead to more nonsense.

“I think whatever we do that opens the door to more information just means that Adam Schiff’s appetite will never be satisfied, and we have to have some discipline on how long we extend this nonsense,” Cramer said.

Schiff, the lead House impeachment manager, said Republicans are still reeling from the revelations in Bolton’s book and noted the “abrupt” end Tuesday to Trump’s defense case.

"I don’t think, frankly, that we could have made as effective a case for John Bolton’s testimony as the president’s own lawyers,” said Schiff, D-Calif.

Republican senators have bashed the House for not subpoenaing Bolton and other witnesses up front and said it’s not the Senate’s job to remedy an incomplete case. But, Schiff said there was little to gain on subpoenaing Bolton because a court fight could have tied up the case for years.

Trump’s defense team finished its arguments before the Senate much quicker than expected Tuesday before GOP senators huddled in a room in the Capitol on a path forward. The trial is set to resume Wednesday with 16 hours of questions to both sides. That would set up a vote likely on Friday on the big looming question of whether to open the trial up to new witnesses or documents. Democrats would need four GOP votes.

“The witness vote I think could easily be close," Sen. Ted Cruz, R-Texas, said. "We just came from a conference in which there was vigorous discussion and debate on the question of whether additional witnesses are needed.”

As the manuscript viewing was floated as a way around seeing Bolton testify, some senators argued nothing replaced taking testimony from Bolton under oath.

“I’d like to hear from Mr. Bolton," Romney said when asked if the manuscript would satisfy him.

He added that he could not predict whether three other GOP senators would vote for witnesses and signaled Tuesday it’s still a volatile situation. “I don’t think they’re all settled as a group or as individuals as to exactly how they're going to vote,” Romney said.

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While Graham would prefer to conclude the trial without witnesses, he said if the door was open to witnesses, there was "consensus" Republicans wanted more than just Bolton, but the Bidens, the whistleblower and more.

“If you call John Bolton, we’re calling everybody,” Graham said.

Fox News' Jason Donner, Gregg Re, Mike Emanuel, Liz Friden, Chad Pergram and Fox Business’ Hillary Vaughn contributed to this report.