'If you have a rigged trial there's no exoneration in acquittal': Sen. Chris Van Hollen Pelosi and McConnell have been at an impasse over the Senate impeachment trial.

Republican Alaska Sen. Lisa Murkowski put her finger on a key issue of an impeachment trial when she expressed concern about the Senate leadership coordinating with the White House on the trial, according to one top Democrat.

"Is Sen. Mitch McConnell, the Republican leader, going to try to rig this trial, working in lockstep with the president and his lawyers? Or is he going to allow a fair trial?" Sen. Chris Van Hollen, D-Md., said on ABC's "This Week" Sunday. "We keep hearing President Trump say he's going to be exonerated. Look, if you have a rigged trial there's no exoneration in acquittal."

ABC News Chief White House Correspondent Jonathan Karl asked Van Hollen if Democrats would be able to convince Republican senators to vote with them, but Van Hollen said it was too early to see how Murkowski and others would vote.

"They're going to have to answer for the fact that they don't want to see anymore evidence, right?" he said. "Those who vote against witnesses and vote against documents are essentially telling the American people they don't want to see anything. They don't want to hear anything. And in doing so, you're complicit in a cover-up."

President Donald Trump became the third president in U.S. history to be impeached earlier this month, but House Speaker Nancy Pelosi has not yet delivered the articles of impeachment to the Senate.

Pelosi has said that she will not transmit the articles until she sees "the process that is set forth in the Senate."

McConnell, the Senate majority leader, and Senate Minority Leader Chuck Schumer have been at an impasse over the structure of the trial, namely whether the Senate would call witnesses.

"The witnesses and documents are the main arguments here," Schumer said at a press conference on Monday. "We must decide them and hopefully we can decide them in a bipartisan way before going forward with the trial."

In an interview with Fox News, McConnell said, "Everything I do during this, I'm coordinating with White House counsel. There'll be no difference between the president's position and our position as to how to handle this."

Murkowski said on Tuesday that she was "disturbed" by McConnell's saying that he would work in coordination with the White House on an impeachment trial.

"When I heard that I was disturbed," she told Alaska NBC affiliate KTUU. "To me it means that we have to take that step back from being hand in glove with the defense, and so when I heard what Leader McConnell has said, I happened to think that further confused the process."

Even if Democrats are unable to get the votes for a Senate trial with witnesses, Van Hollen said Pelosi would eventually send over the articles of impeachment so the trial could take place.

"She's been very clear there will be a trial," he said. "And so, yes, she will be sending over the articles of impeachment. I think, right now, we're engaged in this conversation about the importance of being able to call witnesses."

As for when those articles will make their way to the other side of the Capitol, the decision would be up to Pelosi, the senator said.

While Van Hollen said that the House had produced a lot of evidence supporting impeachment, in a Senate trial House managers should have the right to display additional evidence.

"Why is it that Mitch McConnell seems to say he doesn't want to call any witnesses? That is clearly taking the position that you don't want to see the evidence. And that is irresponsible, and I think it's an abdication of his constitutional responsibility," he said.

ABC News' Mariam Khan contributed to this report.