Vermont Senator Patrick Leahy is urging fellow senators to be impartial judges if and when the articles of impeachment make it to their chamber.

In an op-ed in Monday's New York Times he says "A sham trial is in no one's interest" and "a choreographed trial exonerates no one."

"How the Senate handles the coming trial will shape both the presidency and our constitutional system of checks and balances for decades, long after Mr. Trump leaves office," Leahy wrote.

Leahy said he'd like to hear from Acting White House Chief of Staff Mick Mulvaney, former National Security Adviser John Bolton and White House budget official Michael Duffey.

Senate Majority Leader Mitch McConnell has said the Senate trial might not include witnesses at all.

Meanwhile, Senate minority leader Chuck Schumer sent a letter to his colleagues Monday saying a new email released from OMB's Michael Duffy that put a hold on Ukriane is evidence the White House needs to release more documents and witnesses related to the impeachment case.

"A top administration official, one we requested, is saying stop the aid, 91 minutes after Trump called Zelensky, and said keep it hush-hush. What more do you need?" Schumer said.

A White House official tells CBS News the email was one of several related to Ukraine aid and that the hold was in place before the July 25th phone call.