WASHINGTON ― The Senate impeachment trial of President Donald Trump kicked off with a protracted, partisan brawl over the admission of new evidence and witness testimony during the proceedings, a sharp contrast to the unanimous 100-0 vote that set the rules for the trial of then-President Bill Clinton two decades ago.

After Democrats on Tuesday moved to subpoena key documents from the White House and State Department, including records about the administration’s decision to withhold military aid to Ukraine, every Senate Republican voted to kill the effort. GOP senators also rejected requests to subpoena testimony from acting White House chief of staff Mick Mulvaney, who the White House had blocked from testifying during the House impeachment investigation, as well as former National Security Adviser John Bolton.

“A trial without evidence is not a trial. It’s a cover-up,” Senate Minority Leader Chuck Schumer (D-N.Y.) said in a floor speech before voting began on the issues.

The fierce procedural drama began after Senate Majority Leader Mitch McConnell (R-Ky.) unveiled a resolution Monday evening laying out the rules of the trial that would have given each side 24 hours over just two days to present their arguments and would not guarantee any witness testimonies.

In a rare concession, however, McConnell made last-minute changes that track more closely with the Clinton trial by allowing more time for opening arguments after Democrats and several Republican senators objected to the original guidelines. The new rules allow both sides 24 hours spread over three days ― not two ― to present their evidence.

Schumer said that Republican senators “felt the heat” from Democrats and pushed for the last-minute changes. “It shows that they can make other changes and that we can get documents and witnesses,” Schumer said. “In other words, this idea that Mitch McConnell, whatever he does, every one of them will go along with, it doesn’t seem to be happening.”

Democrats initially blasted the rules package, accusing McConnell of orchestrating a quick trial that would keep the American people from seeing key evidence, with proceedings potentially running late into the night.

Under the rules authored by McConnell, senators will be able to call for witnesses only after opening arguments from both sides, but ensuring they actually testify will require at least 51 votes. If the Senate doesn’t allow witnesses, the trial could be over by the end of next week.

“There is no guarantee that Leader McConnell will allow these votes to take place later in the trial, so now, before any resolution passes, we must do it,” Schumer said Tuesday.

McConnell defended the rules, which the Senate adopted early Wednesday, saying in a floor speech a day prior that the Senate would “finally” receive “some fairness” in the impeachment process.

Several Republican senators have indicated they are likely to support calling witnesses later in the trial, however, including Sens. Susan Collins of Maine and Mitt Romney of Utah. Democrats will need to convince at least four GOP senators to vote with them to subpoena their desired witnesses.

“I will be in favor of witnesses, I presume, after hearing the opening arguments,” Romney said Tuesday.

Romney said he was not bothered by the prospect of the trial proceeding deep into the night, comparing the situation to his role running the 2002 Winter Olympics in Salt Lake City.

The games were “on a time delay and people got to see” them, Romney said.

Trump is charged with abuse of power for his dealings with Ukraine and his efforts to block congressional investigations. Given GOP control of the Senate, the chamber’s ultimate votes on the two articles of impeachment are widely expected to fall far short of the required two-thirds margin required for removal from office.

The House impeachment managers launched into an aggressive argument on the Senate floor for ousting Trump from office on Tuesday, saying that he tried to “cheat in the (2020) election” by getting Ukraine to announce an investigation into former Vice President Joe Biden, his possible Democratic opponent this November.

Rep. Adam Schiff (D-Calif.), one of the managers, pressed the case for additional witnesses, noting that Trump last month ― in a video clip Schiff played senators ― said he would “love” to have former administration officials testify in his Senate trial.

“The Senate has an opportunity to take the president up on his offer to make his senior aides available,” Schiff said. “But now the president is changing his tune.”

Trump, speaking from the glitzy World Economic Forum in Davos, Switzerland, said Wednesday that he would still “love” to have Mulvaney and others testify, but would leave it up to the Senate to decide.

The president also said allowing Bolton to testify would be a “national security problem” ― a claim that echoes then-President Richard Nixon’s failed attempts to derail his own impeachment trial in the 1970s.

″He knows what I think about leaders,” Trump said of Bolton during a press conference in Davos. “What happens if he reveals what I think about a certain leader and it’s not very positive?”

“I don’t know if we left on the best of terms,” he added, referring to his decision to fire Bolton in September. “I would say probably not. So you don’t like people testifying when they didn’t leave on good terms.”

Trump: I would “rather” have Bolton testify but “the problem with John is that it's a national security problem.” pic.twitter.com/EAVFVGwQxZ — TPM Livewire (@TPMLiveWire) January 22, 2020

Republicans ultimately rejected 11 Democratic amendments on Tuesday over nearly 13 hours of debate on the floor, including motions for subpoenas calling for witness testimony and other documents related to the Ukraine matter.

Senators grew weary of the proceedings late in the night, often ignoring chamber guidelines to remain quiet and in their seats. Both the House managers and Trump’s lawyers earned an admonishment from Supreme Court Chief Justice John Roberts at one point early Wednesday, after a tense exchange that veered into personal attacks.

The trial will continue on Wednesday when the House impeachment managers officially begin their opening arguments in the case.

Sen. Roy Blunt (R-Mo.) expressed skepticism that House managers would use all 24 hours of their allotted time this week, adding that a lot of their arguments presented Tuesday had been repetitive.

“Adam Schiff standing up and saying the same thing five times straight I don’t think is having the impact here he wanted to have,” Blunt told reporters. “They may very well think ... this is the last time the general public will pay attention and they better drive it home.”

Hayley Miller contributed reporting.