“Do you think Chuck Schumer is impartial?” Mr. McConnell asked during an appearance Monday morning on “Fox & Friends.” He went on: “So let’s quit the charade. This is a political exercise.”

With lawmakers at home in their districts for a two-week holiday recess, Mr. Trump’s trial is in limbo. The House voted almost entirely along party lines last week to impeach Mr. Trump on charges of abuse of power and obstruction of Congress in connection with the Ukraine matter.

For a trial to begin, the House must transmit the charges contained in the articles of impeachment to the Senate. But with Mr. McConnell coordinating trial planning with the White House, Speaker Nancy Pelosi is withholding the articles, she has said, until she gets some assurance that the proceedings will be fair.

In his “Fox & Friends” appearance, Mr. McConnell called Ms. Pelosi’s decision to withhold the articles “absurd.” He predicted that she would ultimately back down. “I can’t imagine what purpose is served by her holding on to the papers, so sooner or later I’m assuming she will send them over,” he said.

Mr. McConnell is also unlikely to agree to Mr. Schumer’s demand for documents. He has already rejected Mr. Schumer’s request for testimony from four White House officials: John R. Bolton, Mr. Trump’s former national security adviser; Mick Mulvaney, the acting White House chief of staff; Robert Blair, Mr. Mulvaney’s senior adviser; and Mr. Duffey, the official with the Office of Management and Budget.

Democrats argue that Mr. McConnell, who has said he is “taking my cues” from the White House, is effectively letting Mr. Trump plan his own trial and violating the oath that all senators take to be impartial jurors during an impeachment trial. In his letter demanding new documents, Mr. Schumer took a shot at Mr. McConnell.

“To oppose the admission of this evidence would be to turn a willfully blind eye to the facts, and would clearly be at odds with the obligation of senators to ‘do impartial justice’ according to the oath we will all take in the impeachment trial,” he wrote.