Senate Republicans rejected an effort by Democrats to call White House acting chief of staff Mick Mulvaney to testify at the outset of the impeachment trial.

Democrats forced a vote to get language included in the resolution on the trial rules that would subpoena Mulvaney, who previously defied a subpoena to appear as part of the House impeachment inquiry.

But senators voted 53-47 along party lines to table the amendment, effectively killing it. Democrats needed four Republican senators to support their efforts to get a deal on calling Mulvaney to testify as part of the rules resolution.

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Democrats have vowed to force votes on a slew of amendments on Tuesday to try to shoehorn a deal on potential witnesses and documents related to the delayed Ukraine aid into the Senate's debate on the impeachment rules.

In addition to Mulvaney, Democrats pushed late Tuesday to include language subpoenaing Mulvaney's senior adviser Robert Blair and Michael Duffey, the associate director of national security at the Office of Management and Budget. That effort was also rejected in a party-line vote.

Democrats were later expected to push to include language calling for a subpoena 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. Democrats argue the four witnesses have firsthand knowledge and can shed light on the extent of Trump’s direct involvement in the aid holdup.

Mulvaney in particular has emerged as a central figure in the impeachment investigation; House Democrats subpoenaed him as part of their inquiry, but the White House refused to take part in the months-long probe.

Mulvaney sparked a firestorm, and a multiday cleanup effort, late last year when he appeared to acknowledge that Trump linking Ukraine aid to a probe into the 2016 election was nothing out of the ordinary, telling reporters to “get over it.”

“There’s going to be political influence in foreign policy,” Mulvaney said during a press conference in the White House briefing room. “That’s going to happen.”

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He later accused the media of mischaracterizing his remarks as part of a “witch hunt” against Trump.

Democrats have seized on Mulvaney’s remarks and his involvement in decisions related to the $400 million in security aid to Ukraine that was eventually released.

“The witnesses we request are not Democrats. They’re the president’s own men,” Senate Minority Leader Charles Schumer Chuck SchumerPelosi orders Capitol flags at half-staff to honor Ginsburg Ginsburg in statement before her death said she wished not to be replaced until next president is sworn in Democrats call for NRA Foundation to be prohibited from receiving donations from federal employees MORE (D-N.Y.) said ahead of Tuesday’s vote.

Rep. Hakeem Jeffries Hakeem Sekou JeffriesPelosi: House will stay in session until agreement is reached on coronavirus relief Races heat up for House leadership posts Postmaster general earned millions from company with ties to Postal Service: report MORE (D-N.Y.), one of the House impeachment managers, called Mulvaney “crucial” to the decision to delay the Ukraine aid.

“Mulvaney was at the center of every stage of the president’s substantial pressure campaign against Ukraine. Based on the extensive evidence the House did obtain, it is clear that Mulvaney was crucial in planning the scheme, executing its implementation and carrying out the cover-up,” Jeffries said.

Multiple officials who testified in the House implicated Mulvaney in the decision to delay the Ukraine aid.

Fiona Hill, Trump’s former leading Russia expert, told House investigators that Bolton was so alarmed by what he heard about Trump’s contacts with Kyiv that he instructed her to notify the chief lawyer for the National Security Council about the efforts of Trump's personal lawyer Rudy Giuliani, Mulvaney and Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE, the U.S. ambassador to the European Union.

“I am not part of whatever drug deal Sondland and Mulvaney are cooking up,” Bolton told Hill, according to her reported testimony.

No Republican senator has said they specifically want to hear from Mulvaney or that they would vote to subpoena him later in the trial.

Under the Republican impeachment trial rules, which are expected to be passed by the Senate later Tuesday, there is no guarantee that additional witnesses or documents will be subpoenaed.

Instead, in a win to a coalition of moderate senators, it includes language saying that after opening arguments and questions from senators, there will be a vote on whether it will be in order to call for witnesses.

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Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE (R-Ky.) defended the rules on Tuesday, arguing they would set up a process that was “fair” and “evenhanded.”

“Some outside voices have been urging the Senate to break on this precedent,” McConnell said. “Nobody will dictate Senate procedure to the United States senators.”

White House counsel Pat Cipollone noted that under the rules resolution, the Senate will decide witnesses during a vote next week and urged senators to let the trial get underway.

"We will, I suppose, have this debate again next week, if we ever get there. It's getting late. I would ask you respectively if we could simply start," Cipollone said Tuesday night.

Michael Purpura, a member of the White House team, added to senators, "This chamber's role is not to do the House's job for it."

Updated: 11:19 p.m.