WEST PALM BEACH, Fla. — President Trump spent Christmas Eve morning complaining that Democrats had treated him unfairly during the impeachment inquiry and insisting that Republican leaders in the Senate should run a trial however they see fit.

“It’s up to Mitch McConnell, and we have the majority and now they want McConnell to do wonderful things for them,” Mr. Trump said of Senator Mitch McConnell of Kentucky, the majority leader, during remarks to reporters at his Mar-a-Lago estate. “I mean he’s going to do what he wants to do.”

Lawmakers on Capitol Hill are locked in a dispute over the procedures that will govern a Senate impeachment trial, with Democrats insisting that it must include testimony from witnesses, a decision that Mr. McConnell and other Republicans say is premature.

Mr. Trump has said in the past that he is eager for Republicans to mount a robust defense of his actions during a trial that would include witnesses. But his Republican allies in the Senate have expressed misgivings about creating a circuslike trial. In his remarks on Tuesday, Mr. Trump appeared willing to accept whatever Mr. McConnell decided.