Majority Leader Sen. Mitch McConnell rejected on Tuesday a proposal from Senate Democrats to subpoena four White House officials to testify during President Donald Trump's impeachment trial.

Sen. Chuck Schumer sent a letter to McConnell on Sunday urging the Republican leader to call to testify four witnesses "with direct knowledge of the admin's decision to delay security assistance funding to Ukraine," including White House chief of staff Mick Mulvaney and former national security advisor John Bolton.

The other two officials Schumer has requested are Michael Duffey, associate director for national security at the Office of Management and Budget, and Robert Blair, a senior advisor to Mulvaney.

The White House blocked all four from testifying in the House impeachment inquiry.

"Senate Democrats believe strongly, and I trust Senate Republicans agree, that this trial must be one that is fair, that considers all of the relevant facts, and that exercises the Senate's 'sole Power of Impeachment' under the Constitution with integrity and dignity," Schumer said in the letter.

The impeachment inquiry was triggered by Trump's July 25 phone call with Ukrainian President Volodymyr Zelenskiy in which he pressed his counterpart to announce an investigation into his political rival former Vice President Joe Biden and his son Hunter. At the time, the White House had held up $400 million in military aid and was dangling an official meeting between the two leaders.

McConnell, speaking ahead of Wednesday's expected impeachment vote on the House floor, said that Schumer's letter at first appeared to request the impeachment trial resemble the one held for Bill Clinton in 1999. But, McConnell said, Schumer's requests diverged from previous impeachment proceedings.

"He wants to guarantee upfront that the Senate hear from the very specific witnesses instead of letting the body evaluate the witness issue after, after, opening arguments and senators' questions like back in 1999," he said on the Senate floor. "Very tellingly, our colleague from New York completely omits any motion to dismiss the case, like the one he was happy to vote for himself as a new senator back in 1999."

Following McConnell's opening remarks, Schumer responded, saying he wants both a "speedy and fair trial" and adding that "the leader seems obsessed with speedy and wants to throw fair out the window."

"To simply repeat the arguments that were made in the House and Senate when there are witnesses and documents that could shed light on what actually happened, why not have them?" Schumer said. "We don't know, as I said, what kind of evidence they'll present. It may be incriminating. It may be exculpatory. It may influence how senators vote, it may not. But they certainly must be heard."

McConnell said last Thursday that he intends to work with the White House on the impeachment inquiry. "Everything I do during this, I'm coordinating with the White House counsel," McConnell said in a Fox News interview. "There will be no difference between the president's position and our position as to how to handle this."

Trump has repeatedly criticized the impeachment inquiry, dubbing it a hoax. He once again slammed the impeachment probe in a tweet Monday, saying, "The Impeachment Hoax is the greatest con job in the history of American politics."

Trump tweet

Trump again ripped the impeachment process hours after McConnell's speech on the Senate floor. In a letter to Speaker of the House Nancy Pelosi, he said, "By proceeding with your invalid impeachment, you are violating your oaths of office, you are breaking your allegiance to the Constitution, and you are declaring open war on American democracy."

His administration prohibited White House officials from appearing at impeachment hearings held by House committees. Trump has denied any wrongdoing.

If Trump is impeached by the House, the Senate is expected to begin a trial in January.