PALM BEACH, Fla. >> President Donald Trump lashed out today as his Senate impeachment trial remains at an impasse, with Republican and Democratic leaders at odds over its format and whether witnesses should be called.

Speaking at his Mar-a-Lago club in Palm Beach, Florida after a teleconference call with troops stationed across the globe, Trump singled out Speaker Nancy Pelosi, who is indefinitely holding up sending the articles of impeachment the House passed last week to the Republican-controlled Senate.

“She hates the Republican Party,” Trump charged on Christmas Eve.

Trump has long seen a Senate trial, where he is almost certain to be acquitted, as an opportunity for vindication after he became the third president in the nation’s history to be impeached by the House.

“They treated us very unfairly and now they want fairness in the Senate,” Trump complained of Democrats, adding that he will leave it to Senate Majority Leader Mitch McConnell to do whatever he thinks best.

Pelosi has said she is waiting until she receives more clarity from McConnell about what a trial will look like. He has said he has not ruled out calling witnesses but has also indicated that he is in no hurry to seek new testimony either. Meanwhile the Senate’s top Democrat, Chuck Schumer of New York, has countered that any trial without witnesses would be “Kafkaesque” and a “sham.”

“Let’s put it like this: If there are no documents and no witnesses, it will be very hard to come to an agreement,” Schumer told The Associated Press on Monday.

Schumer is demanding witnesses who refused to appear during House committee hearings, including acting White House chief of staff Mick Mulvaney and former national security adviser John Bolton.

McConnell, who has all but promised a swift acquittal of the president, has resisted making any guarantees and has cautioned Trump against seeking the testimony of witnesses for fear of prolonging the trial. Instead, McConnell appears to have secured Republican support for his plans to impose a framework drawn from the 1999 impeachment trial of President Bill Clinton.

“We haven’t ruled out witnesses,” McConnell said Monday in an interview with “Fox and Friends.” “We’ve said let’s handle this case just like we did with President Clinton. Fair is fair.”

That trial featured a 100-0 vote on arrangements that established two weeks of presentations and argument before a partisan tally in which Republicans, who held the majority, called a limited number of witnesses. But Democrats now would need Republican votes to secure witness testimony — and Republicans believe they have the votes to eventually block those requests.

In a letter Monday to all senators, Schumer argued that the circumstances in the Trump trial are different from those of Clinton’s, who was impeached after a lengthy independent counsel investigation in which witnesses had already testified numerous times under oath. Schumer rejected the Clinton model, saying waiting until after the presentations to decide on witnesses would “foreclose the possibility of obtaining such evidence because it will be too late.”

Schumer also demanded that the Senate, besides receiving testimony, also compel the Trump administration to turn over documents and emails relevant to the case, including on the decision to withhold military aid from Ukraine. He told the AP that Democrats aren’t trying to delay but are simply asking for information directly relevant to the charges in the impeachment articles.

He said that if McConnell won’t agree, “we can go to the floor and demand votes, and we will.”

Pelosi has delayed sending the articles of impeachment to the Senate in hopes of giving Schumer more leverage in talks with McConnell. But the White House believes Pelosi won’t be able to hold out much longer, and the impasse between the Senate leaders leaves open the possibility of a protracted delay until the articles are delivered.

Trump has called the holdup “unfair” and asserted, wrongly, that Democrats were violating the Constitution, as the delay threatened to prolong the pain of impeachment and cast uncertainty on the timing of the vote Trump is set to claim as vindication.

“Pelosi gives us the most unfair trial in the history of the U.S. Congress, and now she is crying for fairness in the Senate, and breaking all rules while doing so,” Trump tweeted Monday from his private club in Palm Beach, Florida, where he is on a more than two-week holiday vacation. “She lost Congress once, she will do it again!”

White House officials have also taken to highlighting Democrats’ arguments that removing Trump was an “urgent” matter before the House impeachment vote, as they seek to put pressure on Pelosi to send the articles of impeachment to the Senate.

At one point, Trump had demanded the testimony of witnesses of his own, like Democrats Joe Biden and his son Hunter, and the intelligence community whistleblower whose complaint sparked the impeachment probe. But he has since relented after concerted lobbying by McConnell and other Senate Republicans who pushed him to accept the swift acquittal from the Senate and not to risk injecting uncertainty into the process by calling witnesses.

The Constitution requires a two-thirds majority in the Senate to convict in an impeachment trial — and Republicans have expressed confidence that they have more than enough votes to keep Trump in office.

A separate but related fight flared Monday in the courts, where the House Judiciary Committee held open the possibility of adding to the articles of impeachment against Trump depending on whatever testimony it can obtain from former White House counsel Don McGahn. The committee also said that testimony from McGahn could be useful in any Senate impeachment trial.

A federal appeals court is set to hear arguments on Jan. 3 on whether to force McGahn to comply with the subpoena.