Fox News senior judicial analyst Judge Andrew Napolitano explained Tuesday that an impeachment trial in the Senate is supposed to be non-political and based solely on the evidence, laying out the "unusual" role of Supreme Court Chief Justice John Roberts.

"This is very unusual. He's the chief justice of the Supreme Court of the United States. He's going to be making rulings, but the jurors can overrule him ... The jurors are the senators," Napolitano told “Fox & Friends.”

Senators can overrule a decision by Roberts during the course of the trial if they have 51 votes to do so. The judge explained that if 51 votes are not available, then key decisions will be left to Roberts' sense of "fairness and dignity and intellect."

SCHUMER SAYS HE WANTS IMPEACHMENT TRIAL FOCUSED ON FACTS, NOT 'CONSPIRACY THEORIES,' AS HE BALKS AT GOP CALLING WITNESSES

Senate Minority Leader Chuck Schumer, D-N.Y., said during a news conference Monday that any Senate impeachment trial should be “focused on the facts that the House presented, not on conspiracy theories” – an apparent slight at Republican attempts to alleviate blame on President Trump by casting aspersions on former Vice President Joe Biden and his son Hunter’s business dealings in Ukraine.

In his letter to McConnell, the New York Democrat specifically asked that four witnesses be called during the trial: Mick Mulvaney, the acting White House chief of staff; Robert Blair,  a senior Mulvaney adviser; John Bolton, the former nation-security adviser; and Michael Duffey of the Office of Management and Budget.

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Napolitano said Trump wants a trial to be held so he can be "vindicated on the merits," rather than have the Senate approve a motion to dismiss the articles of impeachment before a trial can be initiated.

But he said it would be "unusual" for a witness to testify at the Senate trial without having previously given testimony during House proceedings. Napolitano added, however, that an impeachment trial does not work like a normal civilian jury trial.

"In the House, they can vote to impeach because their conscience or their political gut tells them they have the votes to do it and they think the president is unworthy of office. But in the Senate, they take an oath to vote only on the basis of the evidence and not on politics or any other external influence. ... The oath is required by the Constitution and we'll see how seriously they take that oath," Napolitano said.

Fox News' Andrew O'Reilly contributed to this report.