WASHINGTON (AP) — The U.S. Senate plunged into President Donald Trump’s impeachment trial on Tuesday, with Republicans abruptly abandoning plans to cram opening arguments into two late-night sessions and Democrats arguing to subpoena more witnesses.

The trial quickly burst into a partisan fight at the Capitol as the president’s lawyers opened arguments Tuesday in support of McConnell’s plan. Democrats objected loudly to McConnell’s initially proposed rules, and some Republicans made their concerns known in private at a GOP lunch.

Without comment, the Republican leader quietly submitted an amended proposal after meeting behind closed doors with his senators as the trial opened. The handwritten changes would add the extra day and allow House evidence to be included in the record.

The turn of events was a setback for McConnell and the president’s legal team, exposing a crack in the GOP ranks and the growing political unease over the historic impeachment proceedings unfolding in an election year.

A spokeswoman for Republican Sen. Susan Collins said that she and others had raised concerns. The Maine senator sees the changes as significant improvements, said spokeswoman Annie Clark. Though is still deep disagreement about calling additional witnesses.

Opening day stretched deep into the night. Senators remained as the clock passed 9:30 p.m., while Democrats pursued what may be their only chance to force senators to vote on hearing new testimony.

However, Republicans turned back Democratic amendments to subpoena documents from the White House, State Department and budget office, with more votes expected rejecting key witnesses with a front-row seat to Trump’s actions.

By the same 53-47 party-line vote, senators turned aside the Democrats request to subpoena acting White House chief of staff Mick Mulvaney.

Before Chief Justice John Roberts gaveled in the session Tuesday, Democrats warned that the rules package from Trump’s ally, McConnell, could force midnight sessions that would keep most Americans in the dark about the trial.

“This is not a process for a fair trial, this is the process for a rigged trial” Rep. Adam Schiff (D-Caif.), the chairman of the House Intelligence Committee leading the prosecution, told reporters.

He called it a “cover-up.”

The first test came at midday as the senators begin to debate and vote on McConnell’s proposed rules. Republican senators are fell in line behind his plan.

“Sure it will be a fair trial when you’ve got 24 hours of arguments on both sides,” Sen. Chuck Grassley of Iowa told state reporters on a conference call.

The Democrats say the prospect of middle-of-the-night proceedings, without allowing new witnesses or even the voluminous House records of the trial, will leave the public without crucial information about Trump’s alleged political pressure campaign on Ukraine and the White House’s obstruction of the House impeachment probe.

“The McConnell rules seem to be designed by President Trump for President Trump,”said the Senate Democratic leader, Chuck Schumer. “It almost seems the resolution was written in the White House, not the Senate.”

Trump himself, in Davos, Switzerland, for an economic conference, denounced the proceedings as “a total hoax," and said, “I’m sure it’s going to work out fine.”

The rare impeachment trial is unfolding in an election year with senators deciding whether Trump’s actions warrant removal at the same time that voters are forming their own verdict.

If the senators agree to McConnell’s proposal for speedy trial and acquittal, Schiff said, “iIt will not prove the president innocent, it will only prove the Senate guilty of working with the president to obstruct the truth from coming out.”′

Rep. Jerry Nadler, the Judiciary Committee Chairman also leading the House team, said: “There’s no trial in this country where you wouldn’t admit relative witnesses.”

Trump’s presidency is on the line, and the nation is deeply divided just weeks before the first Democratic primary presidential contests.

Four senators who are also presidential candidates will be off the campaign trail, seated among the other senators as jurors.

McConnell had promised to set rules similar to the last impeachment trial, of President Bill Clinton in 1999, but his resolution diverged in key ways. On the night before the trial, he offered a compressed calendar as Trump’s lawyers argued for swift rejection of the “flimsy” charges in a trial that never should have happened.

“All of this is a dangerous perversion of the Constitution that the Senate should swiftly and roundly condemn,” the president’s lawyers wrote in their first full filing Monday. “The articles should be rejected and the president should immediately be acquitted.”

Democrats — as the House prosecutors practiced opening arguments well into the night on the Senate floor — vowed to object to a speedy trial as they pressed for fresh witnesses and documents.

“It’s clear Sen. McConnell is hell-bent on making it much more difficult to get witnesses and documents and intent on rushing the trial through,” Schumer said.

The first several days of the trial are expected to be tangled in procedural motions playing out on the Senate floor and behind closed doors. Senators must refrain from speaking during the trial proceedings.

Like Trump and the Senate presidential candidates, House Speaker Nancy Pelosi will also be away for the proceedings, leading a bipartisan congressional delegation to Poland and Israel to commemorate the 75 years since the liberation of Auschwitz at the end of World War II.

She issued a statement Tuesday denouncing McConnell’s proposed ground rules as a “sham” because of the compressed schedule and lack of guarantee that witnesses will be called or that evidence gathered by the House would be admitted in the Senate trial.

“The Senate GOP Leader has chosen a cover-up for the President, rather than honor his oath to the Constitution,” Pelosi said.

Also Tuesday, the House Democratic managers overseeing the impeachment case asked White House Counsel Pat Cipollone, the president’s lead lawyer at the trial, to disclose any “first-hand knowledge” he has of the charges against Trump. They said evidence gathered so far indicates that Cipollone is a “material witness” to the allegations at hand.

House Democrats impeached the Republican president last month on two charges: abuse of power by withholding U.S. military aid to Ukraine as he pressed the country to investigate Democratic rival Joe Biden, and obstruction of Congress by refusing to cooperate with their investigation.

The Constitution gives the House the sole power to impeach a president and the Senate the final verdict by convening as the impeachment court for a trial.

The president late Monday named eight House Republicans, some of his fiercest defenders, to a special team tasked with rallying support beyond the Senate chamber in the court of public opinion.

Four TV monitors were set up inside the Senate chamber to show testimony, exhibits and potentially tweets or other social media, according to a person familiar with the matter but unauthorized to discuss it on the record.

The White House document released Monday says the two charges against the president don’t amount to impeachable offenses. It asserts that the impeachment inquiry, centered on Trump’s request that Ukraine’s president open an investigation into Democratic rival Biden, was never about finding the truth.

No president has ever been removed from office. With its 53-47 Republican majority, the Senate is not expected to mount the two-thirds voted needed for conviction. Even if it did, the White House team argues it would be an ”’unconstitutional conviction″ because the articles of impeachment were too broad.