Sen. Dick Durbin (D-Ill.) said Sunday there may be no witnesses to exonerate President Trump based on the White House's reluctance to provide evidence as part of the ongoing impeachment probe.

Durbin said the administration has attempted to deny the House's evidence regarding allegations against Trump, noting the White House turned down House Judiciary Committee Chairman Jerrold Nadler's (D-N.Y.) invitation to be part of the panel's hearings.

"It appears to me there are no witnesses the president would want to call to exonerate himself. Maybe such a witness doesn't exist. I don't know," Durbin said on CBS's "Face the Nation."

"The bottom line is if we are going to have an actual trial, we should consider evidence, and that's why I think [Senate Minority Leader Charles] Schumer [D-N.Y.] and [Senate Majority Leader Mitch] McConnell [R-Ky.] need to sit down and have an orderly respectable process in the senate," he added.

He said Schumer and McConnell have to sit down to ensure the trial happens in a "proper bipartisan way."

"That hasn't happened yet," Durbin added.

The Senate is expected to hold a trial in January, following an expected House vote this week on articles of impeachment.

No Republican senators have publicly stated that they support convicting and removing Trump from office, and McConnell has said he'll be in "total coordination" with the White House on the trial.