Senate Majority Leader Mitch McConnell changed the resolution laying out the rules of President Donald Trump’s impeachment trial shortly before it began on Tuesday amid concerns from some key Senate Republicans and an uproar from Democrats.

The new resolution will give the House impeachment managers and the President’s team three days each to make their 24 hours of trial arguments, instead of two as McConnell had initially proposed. There were also changes to the section of the resolution that would not have admitted the House’s evidence without a vote — now, evidence will be admitted automatically unless there is a motion from the President’s team to throw out evidence.

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Supreme Court Chief Justice John Roberts read aloud the new version of the resolution to start the impeachment trial in earnest on Tuesday, and a heated debate over the rules — and more importantly, seeking witnesses and documents during the trial — is expected despite the concessions from McConnell.

Two GOP aides said the changes McConnell made were the result of concerns from moderate Republicans. The alterations were hand-written into the resolution — a sign they were hastily put together before the trial began early afternoon Tuesday.

Republican Sen. Susan Collins of Maine and other colleagues “raised concerns about the 24 hours of opening statements in two days and the admission of the House transcript is the record,” Annie Clark, a Collins spokeswoman, told CNN. “Her position has been that the trial should follow the Clinton model as much as possible. She thinks these changes are a significant improvement.”

The move is a sign of how closely McConnell, who cannot afford to lose more than four GOP senators to keep control of the trial, is keeping the pulse of the moderates in his conference.

Democrats erupted when McConnell’s four-page organizing resolution was released Monday night, dividing 24 hours over two days for opening arguments, delaying the question of witnesses until after the arguments were completed and requiring a vote for the House evidence to be submitted. Despite the changes, Democrats on Tuesday pushed for the Senate to obtain documents and witness testimony at the outset.

“If the Senate votes to deprive itself of witnesses and documents, the opening statements will be the end of the trial,” House Intelligence Chairman Adam Schiff, the lead impeachment manager and California Democrat, said during the trial debate Tuesday. “So to say, ‘Let’s just have the opening statements and then we’ll see’ means let’s have the trial, and maybe we can just sweep this all under the rug.”

Senate Minority Leader Chuck Schumer plans to offer amendments to the resolution, including for the Senate to seek witnesses and documents in the trial. Schumer is pushing for the Senate to subpoena witnesses and documents at the outset, and not after the arguments are made, arguing that Republicans are coordinating with the President to rush to the trial’s conclusion. His first amendment, which will be debated Tuesday afternoon, would be to subpoena documents from the White House related to Ukraine.

“The McConnell rules seem to be designed by President Trump for President Trump. It asks the Senate to rush through as fast as possible and makes getting evidence as hard as possible,” Schumer said on the Senate floor Tuesday. “The McConnell resolution will result in a rushed trial with little evidence in the dark of night.”

But McConnell said on the Senate floor before the trial began that he has the votes from Republicans to move forward. McConnell said his proposal tracked closely with President Bill Clinton’s 1999 impeachment trial that was “fair, even-handed and tracks closely with past precedents.”

Impeachment guide: Voting on the trial rules

“Here in the Senate, the President’s lawyers will finally receive a level playing field with the House Democrats, and will finally be able to present the President’s case,” McConnell said.

Key GOP moderates like Sens. Lamar Alexander of Tennessee and Mitt Romney of Utah said Monday they would back McConnell’s proposed rules. McConnell worked with his moderate members to include language in the resolution that includes a vote on whether the Senate should subpoena witnesses and documents — but later in the trial.

“Overall, it aligns closely with the rules package approved 100-0 during the Clinton trial,” Romney said of McConnell’s proposed rules. “If attempts are made to vote on witnesses prior to opening arguments, I would oppose those efforts.”

White House counsel Pat Cipollone, who is leading the President’s defense, said the President’s team backed the resolution.

“We believe that once you hear those initial presentations, the only conclusion will be that the President has done absolutely nothing wrong,” Cipollone said. “And that these articles of impeachment do not begin to approach the standard required by the Constitution.”

Trump is in Davos, Switzerland, for the Davos World Economic Forum, but he still weighed in on Twitter when the trial started on Twitter. “READ THE TRANSCRIPTS!” he wrote.

Debate could go into closed session

Tuesday’s session will be the first substantive day in the Senate trial after the House impeached Trump last month for abuse of power and obstruction of Congress. House Democrats charge that the President abused his office by withholding US security aid and a White House meeting while pressuring Ukraine to investigate his political rivals, and then covered it up by obstructing the impeachment inquiry.

The House impeachment managers and the President’s legal team will debate the resolution on the Senate floor when the trial gavels in at 1 p.m. ET. There will be two hours of debate for the McConnell’s resolution and then two hours of debate for Schumer’s amendment. When senators want to debate the resolution themselves, they will have to go into closed session, removing the public and the media from the chamber, something that’s expected to occur on Tuesday.

While the main debate on Tuesday is over the rules of the trial, House Democrats also opened up another front in the fight with the President’s legal team, accusing White House counsel Pat Cipollone of being a “fact witness” in the President’s Ukraine scheme.

“You must disclose all facts and information as to which you have first-hand knowledge that will be at issue in connection with evidence you present or arguments you make in your role as the President’s legal advocate so that the Senate and chief justice can be apprised of any potential ethical issues, conflicts, or biases,” the House impeachment managers wrote to Cipollone.

The White House dismissed the House’s allegations.

“House Democrats are trying to run one of the President’s strongest advocates off the case before it even starts,” Ueland said. “They won’t succeed.”

From 1999 to now

Since the House passed the two articles of impeachment last month, McConnell has said he would follow the precedent of Clinton’s 1999 impeachment trial. McConnell has pointed to the fact that the Senate put off the question of witnesses until later in the trial, after opening arguments and the senators’ period for asking questions had concluded. At that point, three witnesses were deposed, and portions of those depositions were played in the Senate chamber.

McConnell’s resolution similarly puts the question of witnesses until after each side has 24 hours for their opening arguments — split over three days now, instead of two — and 16 hours of Senate questions. At that point, the Senate will vote generally on whether it should seek witnesses and documents, and then it will consider individual witnesses.

But Democrats say there are key differences. The Senate’s Clinton witnesses had already testified before the grand jury, while the witnesses Democrats are now seeking — former national security adviser John Bolton, acting White House chief of staff Mick Mulvaney, White House budget official Michael Duffey and White House aide Rob Blair — refused to testify during the House’s impeachment inquiry.

Democrats have also pointed to other divergences from Clinton as a sign McConnell is trying to rush the trial. The Clinton trial still provided four days per side for opening arguments, though splitting it up over three days means it’s unlikely the sessions will stretch beyond midnight as initially expected.

Schiff on Tuesday cited the documents Democrats are seeking from the Trump administration as the most important pieces of evidence to still obtain.

“If we’re truly interested in fair trial, the first step ought to be the production of the documents,” Schiff said. “Those will reveal precisely who the most important witnesses are.”

This story has been updated with additional developments Tuesday.