Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) is struggling to maintain control of President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE’s impeachment trial following news of former national security adviser John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE’s bombshell manuscript.

McConnell on Monday deflected growing calls, including from fellow GOP senators, to allow testimony from Bolton and other potential witnesses, which could prolong the trial and deal a massive blow to Trump and Republicans.

Senate debate over whether to call additional witnesses was upended Sunday following a New York Times report revealing that Bolton claims in a draft of his forthcoming book that Trump told him directly he wanted to freeze U.S. assistance to Ukraine to spur an investigation of former Vice President Joe Biden Joe BidenMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE.

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McConnell’s strategy all along has been to keep the trial as short as possible and avoid giving more political ammo to Democrats to use against Trump and vulnerable Republican senators in the November elections.

The GOP leader urged fellow Republicans at a lunch meeting Monday to keep their powder dry and not make a decision on the need to subpoena witnesses and documents until the end of next week, after Trump’s defense team has presented its arguments and senators have had a chance to ask questions on the Senate floor.

McConnell told colleagues that they don’t need to answer persistent media questions about additional subpoenas until phase one of the trial is complete, as outlined in the organizing resolution passed last week by all 53 Republican senators, according to senators at the meeting.

Sen. Kevin Cramer Kevin John CramerMomentum growing among Republicans for Supreme Court vote before Election Day On Paycheck Protection Program, streamlined forgiveness is key McConnell shores up GOP support for coronavirus package MORE (R-N.D.), who attended the lunch, said McConnell told GOP senators to “remember we passed a rules package that gives us an opportunity to vote on this very issue of witnesses after we hear both sides and ask our questions.”

“He just reiterated that a couple times, as did some other people, just to remind us that we have dealt with this and we don’t have to deal with the next step of it until the end of phase one,” Cramer added.

“Take a breath, we’re going to vote on witnesses,” said Senate Republican Conference Chairman John Barrasso John Anthony BarrassoOVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium Senators reach compromise on greenhouse gas amendment stalling bipartisan energy bill The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump, Biden battle over vaccine, economy; Congress returns MORE (Wyo.), noting that Trump’s lawyers have one more day of presentations followed by 16 hours for senators to ask questions.

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McConnell’s strategy has been working so far, but there’s little room for error, making the Bolton news all the more challenging for the Kentucky Republican.

Two key Republicans — Sens. Mitt Romney Willard (Mitt) Mitt RomneyMomentum growing among Republicans for Supreme Court vote before Election Day Toobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote The Memo: Court battle explodes across tense election landscape MORE (Utah) and Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (Maine), who faces a tough reelection bid — on Monday indicated they are more likely to support additional witness testimony. Romney made a forceful case at the Republican lunch for calling Bolton to testify, but it didn’t appear to immediately change any opinions.

He told reporters earlier in the day that it’s “increasingly likely that other Republicans will join those of us who think we should hear from John Bolton,” but that statement was slapped down by newly appointed Sen. Kelly Loeffler Kelly LoefflerTrump supporters chant 'Fill that seat' at North Carolina rally Vulnerable GOP incumbents embrace filling Supreme Court seat this year Georgia GOP Senate candidates cite abortion in pushing Ginsburg replacement MORE (R-Ga.).

“Sadly, my colleague @SenatorRomney wants to appease the left by calling witnesses who will slander @realDonaldTrump during their 15 minutes of fame. The circus is over. It’s time to move on!” Loeffler tweeted.

Separately, Sen. Pat Toomey Patrick (Pat) Joseph ToomeyAppeals court rules NSA's bulk phone data collection illegal Dunford withdraws from consideration to chair coronavirus oversight panel GOP senators push for quick, partial reopening of economy MORE (R-Pa.) has floated the possibility of accepting Bolton’s testimony in exchange for a witness who could help Trump’s case, such as Joe Biden's son Hunter Biden.

Other potential swing votes on subpoenaing more witnesses and documents include GOP Sens. Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (Ohio), Jerry Moran Gerald (Jerry) MoranLobbying world This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans Hillicon Valley: Zuckerberg acknowledges failure to take down Kenosha military group despite warnings | Election officials push back against concerns over mail-in voting, drop boxes MORE (Kan.) and Cory Gardner Cory Scott GardnerJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Gardner on court vacancy: Country needs to mourn Ginsburg 'before the politics begin' MORE (Colo.), a vulnerable Republican up for reelection this year. Four defections would allow Democrats to introduce new evidence in the trial through witness testimony and administration records.

But McConnell has declined to endorse the plan floated by Toomey, preferring instead to wait and debate the question of witnesses. Senate Minority Leader Charles Schumer Chuck SchumerVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-N.Y.) has likewise ruled out any deal that would require the Bidens to testify in exchange for hearing from Bolton or acting White House chief of staff Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE.

Republican leaders last week expressed confidence they would have the votes to block the Democrats’ witness request, but that party unity appeared to be in serious doubt Monday morning.

One Republican senator who requested anonymity to discuss the lunch said there was a lot of anxiety within the GOP conference immediately after news of Bolton’s manuscript.

But the lawmaker said McConnell was able to regain control of the situation at lunch.

“McConnell is a very wise old owl. His take was, ‘We’re going to have two more days of the president’s counsel making their case and then we have Q&A and we’ll see where we are,” the senator said.

By Monday evening, after Trump’s lawyers had spent the afternoon going on offense and raising questions about Hunter Biden’s business dealings in Ukraine, GOP senators were feeling better.

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“Clearly we’re in a lot better frame of mind and a lot better shape than we were,” said a second Republican senator, who requested anonymity to talk about the views of colleagues.

Senate Republican Whip John Thune John Randolph ThuneWhat Senate Republicans have said about election-year Supreme Court vacancies The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump contradicts CDC director on vaccine, masks MORE (R-S.D.) last week indicated the vote on witnesses and additional documents would come in the middle of this week, but GOP leaders are now planning to hold the crucial vote on Friday, allowing more time for the arguments of Trump’s defense team to sink in and the uproar over Bolton’s manuscript to die down.

Two potential swing votes — Sen. Lisa Murkowski Lisa Ann MurkowskiMomentum growing among Republicans for Supreme Court vote before Election Day Collins: President elected Nov. 3 should fill Supreme Court vacancy Barrett seen as a front-runner for Trump Supreme Court pick MORE (R-Alaska) and Sen. Lamar Alexander Andrew (Lamar) Lamar AlexanderToobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote Chamber of Commerce endorses McSally for reelection Trump health officials grilled over reports of politics in COVID-19 response MORE (R-Tenn.), who is retiring at the end of this term — said Monday they would stick to their original plan of waiting until after phase one of the trial to decide on witnesses, as McConnell has urged.

Murkowski said in a tweet Monday afternoon “there is an appropriate time for us to evaluate whether we need additional information,” adding “that time is almost here.”

Alexander highlighted his effort to ensure a vote on witnesses by week’s end.

"I worked with my colleagues to make sure we have a chance after we've heard the arguments, after we've asked our questions to decide if we need additional evidence, and I'll decide that at that time," he said.

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Republican leaders spent much of Monday downplaying Bolton’s claim in hopes of keeping the number of potential Republican defections at two.

As of mid-afternoon Monday, they appeared to have held the line for another day.

Speaking to reporters after the lunch, Cramer said he thinks "it’s about the same as it’s always been” when asked whether sentiments are changing in the GOP conference.

Barrasso said, “I didn’t hear anything new at lunch from any member other than what they’ve been saying all the way through the process.”

Murkowski, however, also acknowledged she is "curious" to hear what Bolton has to say.

Democrats think GOP unity on the question of witnesses is starting to crack.

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“This is getting to be a little bit, in this sense maybe, like Watergate. Every few days there’s another revelation and another revelation and another revelation. And the case gets stronger and stronger,” Schumer said Monday afternoon.

Sen. Richard Blumenthal (D-Conn.) said Republicans “are in a real twist,” adding, “They will be held accountable for putting their blinders on.”

Jordain Carney contributed.