Senate Minority Leader Charles Schumer Chuck SchumerPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act Will Democrats attempt to pack the Supreme Court again? Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' MORE (D-N.Y.) on Monday knocked Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellHawley warns Schumer to steer clear of Catholic-based criticisms of Barrett Senate GOP set to vote on Trump's Supreme Court pick before election Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE (R-Ky.), saying he was "totally out of line" after the GOP leader said he would take his cues about the details of an impeachment trial from the White House.

"For him to talk to the president is one thing, for him to say 'I'm going to do just what the president wants' is totally out of line," Schumer said during an interview with CNN's "New Day.

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"Discussion in this kind of situation is not out of the question at all; saying you're going to do just what the president wants is totally out of line," Schumer added.

Schumer sent his opening salvo in negotiations over a Senate trial in a letter to McConnell on Sunday night, laying out what Democrats were asking for as part of a trial expected to start in January.

Schumer wants to call acting White House chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE, his senior adviser Robert Blair, former national security adviser John Bolton John BoltonJudge appears skeptical of Bolton's defense of publishing book without White House approval Maximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales MORE and Office of Management and Budget staffer Michael Duffey to testify as part of a Senate trial.

"We believe all of this should be considered in one resolution. The issue of witnesses and documents, which are the most important issues facing us, should be decided before we move forward with any part of the trial," Schumer wrote in his letter.

Schumer's letter came after McConnell said late last week that he would be in "total coordination" with the White House on his impeachment strategy.

"I wrote this letter because Mitch McConnell seemed to be going off in his own direction and there was no semblance of even discussing a fair, balanced trial where the facts come out," Schumer added on Monday to CNN's "New Day."

He added that he would "prefer" to get a deal with McConnell on the process for the upcoming Senate resolution. Those negotiations have not yet begun.

During the impeachment trial of former President Clinton, senators voted 100-0 on a resolution laying out the process for a trial, but a vote on a subsequent resolution calling for specific witnesses broke down along party lines.