(CNN) Senate Majority Leader Mitch McConnell Tuesday bluntly acknowledged some of the political realities surrounding the upcoming Senate impeachment trial of President Donald Trump, notably saying, "I'm not impartial about this at all."

"I'm not an impartial juror," he said flatly. "This is a political process. There is not anything judicial about it. Impeachment is a political decision."

The frankness of his remarks infuriated Democrats and added to a tension-filled day in the Capitol where senators jockeyed for political leverage ahead of the House impeachment vote Wednesday so they can fulfill their constitutionally prescribed roles as jurors in a trial set to begin in January.

McConnell also predicted the whole exercise will all be for naught because Trump will be acquitted by the GOP-led Senate: "We will have a largely partisan outcome," he said.

Senate Minority Leader Chuck Schumer, a Democrat from New York, said he was "utterly amazed" McConnell would describe himself as not impartial.

"Mitch McConnell said proudly he is not an impartial juror. The American people want Mitch McConnell to be an impartial juror in this situation," Schumer said, before challenging other GOP senators to pledge to be impartial as well.

A reporter challenged Schumer, who has given countless searing speeches on the floor criticizing Trump's actions on Ukraine, if he is really impartial or has already decided Trump is guilty.

"I'm withholding any final decision until we hear all the evidence," Schumer replied. "One of the reasons that we want these witnesses and documents is so that we can hear the full, full length and breadth of what happened. I do not know what these four witnesses will say -- perhaps they'll exculpate Trump, maybe they'll further condemn him," a reference to the four witnesses Schumer had said the Senate needed to hear from in their trial.

Schumer continued, "We don't know the answer to that but before we make any final decisions, any of us, we ought to hear them."

Speaking to reporters after the Senate GOP policy lunch -- where trial procedures were discussed -- McConnell said he thinks he and Schumer should be able reach an agreement on how to run the first part of a trial, when opening statements from House impeachment managers and the President's defense counsel will be delivered and they answer senators' written questions.

But McConnell said he expects to run into partisan gridlock when it comes to the second part of the trial, when tougher decisions need to be made, including whether to call witnesses.

"I'm optimistic that we can agree on phase one," he said. "It's pretty obvious we're likely to disagree on phase two."

At that point, McConnell said, they will have to see "whether there are 51 members of the Senate who want to take one of two directions, either going in the direction of the witnesses or going in the direction of voting on articles of impeachment" and ending the trial.

Earlier in the day, McConnell delivered a tough floor speech during which he rejected Schumer's request to have those witnesses close to Trump testify at the trial. He blasted House Democrats for doing a "sloppy job" in their investigation and said he wouldn't make up for their mistakes by allowing witnesses testify who they should have pursued on their own.

Schumer spoke to reporters after McConnell and criticized the idea of dealing with the trial procedures in two parts. He said all the decisions should be agreed to before the trial begins.

McConnell is just trying to "avoid" and "delay" by saying "let's vote on the easy stuff now and kick the important issues to later," Schumer said. "The key issues here are witnesses and documents, we should decide those from the very beginning."

McConnell noted that during the Senate trial of former President Bill Clinton, a resolution dictating the first part of trial passed 100-0 but votes on the next resolutions dealing with witnesses faced party-line votes.

In another act of political candor, McConnell recognized that both parties are playing political "gotcha" games by digging up 20-year-old quotes that seem to demonstrate senators are changing their views on the need for witnesses based on which party's president is being impeached.

For example, a reporter read McConnell a quote of his from 1999 during the Clinton trial, when McConnell said a GOP House managers' request for witnesses was modest and should be granted, a position that is in contrast to his current opposition to witnesses for the Trump trial.

McConnell smiled and asked the reporter if she had a similar quote to deliver to Schumer when he appeared after him. Yes, she said.

"In a partisan exercise like this, people sort of sign up with their own kind," McConnell said. "And what we may have felt 20 years ago may not be the same as today. You can quote virtually any of us that were here during that period to be on the opposite side because of the nature of the process."