Senate Minority Leader Charles SchumerCharles (Chuck) Ellis SchumerDemocrats question fairness of Senate trial after Graham, McConnell statements Turf war derails bipartisan push on surprise medical bills Senate confirms Trump's nominee to lead FDA MORE (D-N.Y.) said Tuesday he will ask for votes during the impeachment trial calling for witnesses to testify, including acting chief of staff Mick MulvaneyJohn (Mick) Michael MulvaneyConway says White House sees 'no reason' to bow to Democratic witness demands Pro-impeachment group ramps up ads ahead of House vote, Senate trial Schumer says he tried to get McConnell to start impeachment trial talks two weeks ago MORE and former national security adviser John BoltonJohn BoltonConway says White House sees 'no reason' to bow to Democratic witness demands Pro-impeachment group ramps up ads ahead of House vote, Senate trial House Democrats want McGahn testimony even as impeachment moves to Senate MORE.

"I am allowed to ask for votes. I will ask during the impeachment proceeding for a vote on whether Mulvaney should testify, and whether Bolton should testify," Schumer said during an interview with MSNBC.

Schumer predicted that Republicans would be "in a real dilemma" over the efforts by Democrats to get witnesses to testify. A motion to call a witness as part of the Senate trial would only take a simple majority, meaning Democrats need to win over four GOP senators to get to 51 votes.

"Asking for witnesses, something so reasonable ... I expect we'll get a bunch of Republicans to vote with us on these requests," Schumer added.

Senate Majority Leader Chuck SchumerCharles (Chuck) Ellis SchumerDemocrats question fairness of Senate trial after Graham, McConnell statements Turf war derails bipartisan push on surprise medical bills Senate confirms Trump's nominee to lead FDA MORE says he will force votes on Senate floor over witness testimony from WH Chief of Staff Mulvaney, fmr. National Security Adviser Bolton, and others. pic.twitter.com/GMfOrVYYKQ

— MSNBC (@MSNBC) December 18, 2019

Schumer has outlined four witnesses Democrats want to hear from as part of the impeachment trial against President TrumpDonald John TrumpDemocrats secure fast-track to the floor for Canada-Mexico trade deal Mexican official says he's 'very satisfied' with USMCA after recent concern More than 700 historians sign letter calling for House to impeach Trump MORE, which is expected to start in January: Bolton, Mulvaney, Mulvaney's senior adviser Robert Blair and budget staffer Michael Duffey.

Schumer is also asking for one resolution that would be passed at the start of the trial that would determine both the procedure and any specific witnesses that would be called. During the Clinton trial, senators passed two resolutions: one, on the process, and a second calling specific witnesses. 

GOP senators have indicated that they want to delay a decision on witnesses until after the trial has started, similar to the Clinton impeachment. Senate Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellPoll: Support for impeaching and removing Trump dips McConnell tees up votes on 13 Trump judicial picks ahead of break Conway says White House sees 'no reason' to bow to Democratic witness demands MORE (R-Ky.) went a step further on Tuesday and said he doesn't want any witnesses during the trial. 

No GOP senator has backed Schumer's witness request so far.

Sen. Lisa MurkowskiLisa Ann MurkowskiBottom Line Is a trap being set for Trump in the Senate trial? The Hill's Morning Report — Sponsored by AdvaMed — House panel delays impeachment vote until Friday MORE (R-Alaska) told reporters on Tuesday that she hopes McConnell and Schumer come up with a deal, but sidestepped taking a position on witnesses. 

"What has to happen is Senator McConnell and Senator Schumer need to figure out if they can come together with a proposal that we, the Senate, can move forward to support," Murkowski said. 

Sen. Mitt RomneyWillard (Mitt) Mitt RomneyOn The Money: Lawmakers pile on the spending in .4T deal | Trump-Pelosi trade deal creates strife among progressives | Trump, Boris Johnson discuss 'ambitious' free-trade agreement Congress poised to ban tobacco sales to anyone under 21 Bennet, Romney offer compromise proposal amid year-end tax talks MORE (R-Utah), viewed as another potential GOP swing vote, said he was "indifferent" on whether or not the Senate passes one resolution governing both process and witnesses, or handles them in separate resolutions. 

"Leader McConnell apparently wants to do it in two parts," he added.