Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.) said on Monday that she will support a White House-backed criminal justice bill that the Senate is expected to vote on this week.

Harris, a former prosecutor and potential 2020 White House contender, called the bill a "compromise of a compromise" but said she would vote for it because it "takes positive steps to improve our justice system."

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“I have fought to improve our criminal justice system for the better part of my career. This is another step in that direction," Harris said in a statement.

The bill merges a House-passed prison reform bill with a handful of changes to sentencing laws and mandatory minimums for some drug-related felonies.

Supporters last week unveiled a final version of the bill aimed at winning over more GOP support, and the Senate is expected to take an initial vote on the legislation Monday at 5:30 p.m.

Harris said the bill made "long overdue" changes, including retroactively applying the Fair Sentencing Act, but argued that each of the changes to mandatory minimums should apply retroactively — a move that would likely shrink GOP support for the bill.

"All of the Act’s sentencing reforms should be applied retroactively, and the Act should further expand application of earned good time credits, place more prohibitions on private prisons which profit from the incarceration of individuals, and further limit the use of electronic monitoring," Harris added.

Though the bill likely has the votes to pass, Harris's backing marks a major win for supporters of the legislation, who worried the chamber's progressive wing could refuse to support the bill because of 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's endorsement.

Sens. 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 (Ill.), the No. 2 Senate Democrat, and 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.), who is also considered a potential 2020 contender, have been furiously lobbying their colleagues to support the legislation. Booker warned last week that he would be "deeply disappointed" if a Democratic senator voted against it.

"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 at the time. "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."