Senate Republicans blocked Democratic Leader Chuck Schumer’s proposed amendments to Majority Leader Mitch McConnell’s resolution on the rules for the impeachment trial of President Donald Trump.

On Tuesday, Schumer proposed 11 amendments including subpoenas on important documents and witnesses who have first-hand knowledge about Trump’s dealings with Ukraine.

In particular, the Democratic Leader sought Senate approval for subpoenas to obtain all materials related to the Ukraine controversy from the White House, U.S. Department of State, Department of Defense (DOD), and the Office of Management and Budget (OMB).

He also sought approval for subpoenas to obtain the testimony of key witnesses including Acting White House Chief of Staff Mick Mulvaney and former National Security Adviser John Bolton among others.

As expected, Senate Republicans voted along party line (53-47) to table Schumer’s amendments.

Nadler suggested that Senate Republicans were complicit in Trump’s cover-up

Democrats believe that Mulvaney and Bolton are primary figures that could shed light to the Ukraine scandalt that led to Trump’s impeachment. During a press conference in October, Mulvaney admitted that the President delayed the release of almost $400 million in U.S. security assistance to Ukraine to pressure its government to announce an investigation into former Vice President Joe Biden and his son Hunter. In other words, he confirmed a quid pro quo.

At the Senate floor on Tuesday, House Judiciary Committee Chairman Jerrold Nadler (D-New York) said Bolton expressed his willingness to testify in the impeachment trial.

“He's prepared to testify. He says he is relevant evidence not disclosed to the public,” said Nadler, adding that Trump and his fellow Republicans were “afraid” to allow Bolton to testify because “they know he knows too.”

Nadler emphasized that the former National Security is a “firsthand witness” to the President’s abuse of power. He also suggested that if Republicans voted to block Bolton from testifying, they are taking part in a “cover-up.”

“The Senate is on trial in the eyes of the American people…Will you vote to allow all of the evidence to be presented here? Or will you betray your pledge to be impartial juror? Will you bring Bolton here and permit us to present you with the entire record of the President's misconduct? Or choose to be complicit in the President's cover up. So far, I'm sad to say, I see a lot of senators voting for a cover-up,” said Nadler.

He added that Republicans are “voting to deny witnesses and obviously a treacherous vote—a vote against an honest consideration of the evidence against the President—a vote against an honest trial—a vote against the United States.”

White House legal counsel Pat Cipollone condemned Nadler for “making false allegations” against Trump, his team and Senate Republicans.