Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) said on Tuesday that he will bring a bipartisan criminal justice bill up for a vote, marking a significant win for the legislation's supporters, including President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE.

"At the request of the president and following improvements to the legislation that has been secured by several members, the Senate will take up the recently revised criminal justice bill," McConnell said from the Senate floor.

McConnell didn't specify when the Senate will vote but said he will "turn to" the legislation "as early as the end of this week." If the Senate is able to pass the measure, AshLee Strong, a spokeswoman for Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.), said the House "will be ready to act" on the revised bill.

Backers and advocates have been publicly and privately lobbying McConnell for months to bring the bill to the floor, arguing that they have at least 70 votes in support of the legislation. The bill, spearheaded by Sens. Chuck Grassley Charles (Chuck) Ernest GrassleyThe Hill's 12:30 Report: Ginsburg lies in repose Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy Read: Senate GOP's controversial Biden report MORE (R-Iowa) and Dick Durbin Richard (Dick) Joseph DurbinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Grand jury charges no officers in Breonna Taylor death Democrats shoot down talk of expanding Supreme Court MORE (D-Ill.), merges a House-passed prison reform bill aimed at reducing recidivism with four changes to sentencing laws.

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McConnell's remarks are a dramatic turnaround from last week, when he appeared to warn at a Wall Street Journal event that he did not have time to move the criminal justice bill this year, which he said could take up to 10 days.

“It’s extremely divisive inside the Senate Republican Conference, in fact there are more members in my conference that are either against it or undecided than or for it,” McConnell said at the event. “This is a one-week to 10-day bill and I’ve got two weeks.”

McConnell and Cornyn estimated last week that a majority of the conference is either undecided or opposed to the bill. But since then, several Republican senators, including Sens. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (Texas) and David Perdue (Ga.), have publicly endorsed the measure.

In a major win for backers, Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas), McConnell's No. 2, also came out in support of the bill on Tuesday — a move advocates believe could help move other undecided GOP senators.

"I think we'll see a number of Republicans now come on board supporting this bill as amended," Cornyn told reporters. "People now know that we're going to vote on it, it's going to cause people to have to make a decision, but I'm pretty optimistic."

Durbin and Grassley have been circulating a draft that includes changes meant to win over more GOP support. The new version of the bill is expected to be released as soon as Tuesday.

"We've done everything that he and other Republicans have asked us to do: You have to have more than 60 votes. Two weeks ago, we decided that we had to do more compromising. .... You have to have the president on board, we have the president on board," Grassley said, when asked how McConnell got to allowing for a vote.

Grassley also told reporters that McConnell privately pushed back when the Iowa senator said during a recent phone conversation that he thought the Senate GOP leader was opposed to the bill.

"I never heard him say he was against the bill. In fact, in one telephone conversation, I may have suggested he was against the bill. And he said, I have never said I'm against the bill," Grassley recounted.

The changes are expected to include expanding the list of crimes that exclude an individual from bill’s “earned time” credits, which shave time off a prison sentence. Senators are also discussing eliminating a “safety valve” portion of the bill that gives judges some discretion in going around mandatory minimums.

Republican supporters have estimated that they have roughly 30 yes votes within their own caucus. Durbin said on Tuesday that said support within the Democratic caucus was "pretty solid."

"I can't guarantee 100 percent, but it's pretty solid," he added, pressed on a number of supporters.

Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.) added that no Democratic colleagues had told him that the changes aimed at winning over more Republicans would cost him their vote.

"People in my caucus who are progressives who understand ... some elements of the bill, 90 percent of the beneficiaries will be African Americans," Booker said. "I would be deeply disappointed if anybody in our caucus votes against a bill that is going to disproportionally help low-income people and minorities."

McConnell's decision comes days after Trump doubled down on publicly urging the GOP leader to bring up the bill for a vote.

"Hopefully Mitch McConnell will ask for a VOTE on Criminal Justice Reform. It is extremely popular and has strong bipartisan support. It will also help a lot of people, save taxpayer dollars, and keep our communities safe. Go for it Mitch!" Trump said in a tweet last Friday.

Though the criminal justice fight has broad support in both parties, bringing it to the floor tees up a nasty intra-Republican battle with a group of vocal conservative opponents.

Cornyn acknowledged that if opponents force them to go through all the procedural hurdles, it could force the Senate to work up until the end of the year. McConnell, speaking from the Senate floor, warned that without an agreement, senators should be prepared to work between Christmas and New Year's Day.

Cornyn noted that McConnell's Christmas threat "provides a powerful incentive for people to cooperate."

"If we have to jump through all the procedural hoops, we're never going to get all our work done," Cornyn added.

In addition to a swath of Republican senators who have quietly raised concerns about the bill, the measure is also facing fierce opposition from a small group of Republican lawmakers.

Sen. Tom Cotton Tom Bryant CottonGOP brushes back charges of hypocrisy in Supreme Court fight Trump uses bin Laden raid to attack Biden Battle lines drawn on precedent in Supreme Court fight MORE (R-Ark.) has been deeply opposed to the legislation, which he has termed the "jailbreak bill, indicated on Tuesday that he won't go down without a fight on the Senate floor.

"I look forward to debating this bill on the Senate floor and introducing amendments to address its many remaining threats to public safety," Cotton said in a tweet.

Pressed if would object to leadership moving the bill quickly, Cotton said he would let his colleagues decide if "they want to let violent, repeat, serious felons out of prison."

Asked about the Senate working after Christmas, Cotton told reporters as he got in an elevator to go vote: "Merry Christmas."

-updated 12:31 p.m.