Senate Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellImpeachment battle lines harden ahead of pivotal weekKey Trump adviser predicts USMCA will pass Senate as early as Friday GOP rep: Democrats changing their mind on impeachment trial rulesMORE (R-Ky.) is prepared to get Senate Republicans to unilaterally pass a resolution setting the rules for President TrumpDonald John TrumpGolden Globes host Ricky Gervais to celebs: Don’t get politicalTrump says he’ll sanction Iraq if US troops forced to leaveTrump doubles down on threat to Iran cultural sitesMOREs impeachment trial despite John BoltonJohn BoltonImpeachment battle lines harden ahead of pivotal weekNancy Pelosi’s great impeachment charadeMcConnell digs in on impeachment: ‘Non-starter’ for Pelosi to influence trialMOREs statement Monday saying he would testify under subpoena.

The decision by Trumps former national security adviser handed Senate Democrats calling for witnesses to the trial a new talking point, raising pressure on the Senate GOP leader.

Senate Minority Leader Charles SchumerCharles (Chuck) Ellis SchumerThousands take to New York streets in solidarity after anti-Semitic attacks GOP rep: Democrats changing their mind on impeachment trial rulesGraham mulls rule changes to start impeachment trial without articlesMORE (D-N.Y.) on Monday said in a statement that Republicans would be participating in a cover up if they continue to oppose subpoenas, noting that Mr. Boltons lawyers have stated he has new relevant information to share.

Speaker Nancy PelosiNancy PelosiImpeachment battle lines harden ahead of pivotal weekGOP rep: Pelosi is leaving a ‘sad’ legacyGOP rep: Democrats changing their mind on impeachment trial rulesMORE (D-Calif.) said in a tweet responding to news of Boltons willingness to testify that Trump and McConnell had run out of excuses and must allow key witnesses to testify and produce documents Trump has blocked.

One key Republican, Sen. Mitt RomneyWillard (Mitt) Mitt RomneyCongress to clash over Trump’s war powersPelosi’s impeachment tactics are pursuit of power for its own sakeWhy the Wisconsin special election could decide the 2020 presidential electionMORE (Utah), said he wanted to hear from Bolton about what he knows.

But theres no sign yet that any of this will change McConnells calculus.

The GOP leader has repeatedly signaled he wants to follow the precedent set in 1999, when the Senate voted unanimously to begin then-President Clintons impeachment trial without requiring additional witnesses.

McConnell said Monday that the Senate should not change course based on daily developments.

The Senate does not bob along on the current of every news cycle, he said on the Senate floor.

In 1999, every single U.S. senator agreed to establish basic parameters for the start of the trial up front, and we reserved mid-trial questions such as witnesses until later. The vote was 100-0, McConnell argued, sticking firmly to the position he has held in recent weeks.

Sen. John CornynJohn CornynGOP senator plans to seek dismissal of impeachment articlesFive fights awaiting Congress in 2020Republicans came to the table on climate this yearMORE (R-Texas), one of McConnells advisers, said McConnell has reached out to various members of his conference during the holiday break to gauge where they stood on voting for a rules package that simply sets up opening arguments by the House managers and the presidents defense team and  provides time for senators to ask questions.

McConnell told reporters last month that if he couldnt reach a deal with Schumer, he would go to his own conference and ask, Can 51 of us agree how were going to handle this?

Cornyn said that discussion could take place as early as Tuesday during the Senate GOP lunch.

I suspect well probably have a chance to talk about that now that were back in session. Probably tomorrow at lunchtime would be the most logical time to revisit that, Cornyn said.

McConnell is unlikely to hold any vote until Pelosi sends the articles of impeachment to the Senate, said several GOP sources.

Other Republicans are sticking with McConnells view that additional witnesses are not needed at the trial.

The testimony & evidence considered in a Senate impeachment trial should be the same testimony & evidence the House relied upon when they passed the articles of impeachment, Sen. Marco RubioMarco Antonio RubioSunday shows – Pompeo makes rounds in defense of Soleimani strike Rubio: Trump has shown ‘tremendous restraint’ on IranTrump Jr., Ivanka garner support in hypothetical 2024 pollMORE (R-Fla.) tweeted Monday after Boltons statement. Our job is to vote on what the House passed, not conduct an open-ended inquiry.

Sen. Thom TillisThomas (Thom) Roland TillisSchumer aims to drive wedge between Republicans on impeachmentGetting back to basics on the Digital Millennium Copyright ActThe Hill’s Morning Report – Vulnerable Dems are backing Trump impeachmentMORE (R-N.C.), who is up for reelection this year, said Monday he will likely vote against calling additional witnesses.

Sen. Susan CollinsSusan Margaret CollinsImpeachment battle lines harden ahead of pivotal weekCongress to clash over Trump’s war powersPelosi’s impeachment tactics are pursuit of power for its own sakeMORE (R-Maine), who is also up for reelection, said the Senate should follow the 1999 Clinton precedent. 

Senate Rules Committee Chairman Roy BluntRoy Dean BluntPressure builds over impeachment impasse in SenateGOP senator plans to seek dismissal of impeachment articlesPelosi faces decision on articles of impeachmentMORE (R-Mo.) said Boltons statement did not change his mind that the Senate should stick with the Clinton precedent backed by McConnell.

He said it would be preferable if all 100 senators adopted the organizing resolution once they are sworn in as jurors, but that if Democrats oppose it Republicans would rely on votes from their own conference.

Schumer on Monday tried to drive a wedge between McConnell and more moderate members of his GOP conference by vowing to force votes on witnesses and documents, conceding that reaching a deal with McConnell is a long shot.

At the moment, there is a very clear difference between the Republican leader and myself about what it means to have a fair trial, Schumer acknowledged.

He doesnt want a fair trial. He wants a quick and sham trial. Now its up to every senator every senator will have a say in deciding which of the two views wins out. Will we have a fair trial or a cover-up?

Some Senate Republicans say they are open to having Bolton or other witnesses testify later in the trial, but they are backing up McConnells preference to follow the Clinton precedent.

Cornyn on Monday said he has no objection to Bolton testifying by deposition or some pre-recorded testimony. He argued that Boltons testimony could wind up helping Trump.

Asked later if he would vote to call Bolton to testify, Cornyn said, Id keep an open mind.

But he says the time to consider the question is after the opening arguments have been made by both sides.

Romney said of course he would like to hear what Bolton has to say but stopped short of pledging to vote for a subpoena, explaining he wants to know more about the process. 

I would like to be able to hear from John Bolton. What the process is to make that happen, I dont have an answer for you, Romney later added.

Boltons lawyer, Charles Cooper, tantalized Democrats in November when he revealed that his client was personally involved in many of the events, meetings and conversations related to the decision to delay military aid to Ukraine, which is at the core of the House impeachment case.

Cooper said Bolton has knowledge of many relevant meetings and conversations that have not yet been discussed.

The House Intelligence Committee, which led the investigation of Trump in the lower chambers impeachment inquiry, decided not to subpoena Bolton after his lawyer threatened to challenge it in court, which could have delayed the proceedings for weeks or months.

Schumer and Senate Democrats have so far focused their pressure campaign on three other witnesses in addition to Bolton with possible knowledge of Trumps actions related to Ukraine: acting White House chief of staff Mick MulvaneyJohn (Mick) Michael MulvaneyImpeachment battle lines harden ahead of pivotal weekNYT to fight White House’s withholdment of emails about Ukraine aid freezeNancy Pelosi’s great impeachment charadeMORE; Robert Blair, a senior adviser to Mulvaney; and Michael Duffey, the associate director for national security at the Office of Management and Budget.

Jordain Carney contributed.