Donald Trump boosted hopes of federal criminal justice reform on Wednesday by announcing his support for the First Step Act, which seems increasingly likely to get a floor vote in the Senate before the end of the year.

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“We’re all better off when former inmates can re-enter society as law-abiding, productive citizens,” Trump said at the White House. “Americans from across the political spectrum can unite around prison reform legislation that will reduce crime while giving our fellow citizens a chance at redemption.”

The act would expand rehabilitative opportunities for people in prison; ban some of the most startling correctional practices, such as the shackling of pregnant women; and reduce mandatory minimum sentences for a number of drug-related crimes.

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The rare bipartisan effort was bolstered by a letter to senators from public figures including Van Jones, Mark Cuban, Patricia Arquette, Kim Kardashian West and Kanye West. A copy obtained by the Guardian called on Congress to “recognize the humanity” of inmates and declared that “186,000 people in federal prison and their family members” were counting on elected representatives to act.

“The time is now,” the letter said.

The Senate majority leader, Mitch McConnell, must now decide whether to bring the bill up for a vote. He has promised to do so if 60 votes for it can be expected – the amount needed to clear a filibuster. He also said, however, that he will have to see how the legislation “stacks up” with other priorities in the limited time before recess.

As with previous iterations of the bill – which has been in the works since 2015 – negotiations have concerned two components: prison reform and sentencing reform.

Prison reform, which focuses on improving conditions in federal prisons and programs to facilitate re-entry into society, enjoys broad bipartisan support. Sentencing reform, which would remove some harsh sentencing minimums imposed in the 1990s, is favored by Democrats but has fractured Republicans.

First Step passed the House in May with only prison reform included, earning support from virtually all Republicans and more than two-thirds of Democrats. Generally speaking, those Democrats who held out did so on the principle that criminal justice reform legislation must include sentencing reform.

A number of prominent senators, including the Republican judiciary committee chairman, Chuck Grassley, and progressive Democrats, blasted the bill for not including sentencing reform. But the bill had its all-important supporter: Trump. Early in his administration, Trump tasked his top aide and son-in-law Jared Kushner with orchestrating the administration’s work on the issue. At a bipartisan forum on criminal justice reform at the White House, the president promised he would sign the First Step Act.

In the six months after the passage of the House bill, Senate lawmakers led by Grassley set about drafting their own version that could include sentencing reform without alienating Trump or Republican supporters.

That effort appears to have been successful. Late last week the bill earned the support of the national Fraternal Order of Police, which may have helped convince otherwise wavering Republicans.

“We could not have gotten here without the support and feedback of law enforcement,” Trump said on Wednesday.

While conservatives have largely joined progressives in seeking criminal justice reform – it is now a significant plank in the platform promoted by mega-donors Charles and David Koch – many on the right nonetheless remained fearful of being seen as anti-law enforcement.

Jessica Jackson-Sloan, national director for reform advocacy group Cut50, said the process of earning diverse endorsements was delicate and involved substantial concessions on all sides.

“They say bipartisanship is dead and they say working with unlikely allies is dead,” she said. “But I think this bill really shows that when you roll up your sleeves, you negotiate, and you both compromise, this is what can happen.”

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The proposed sentencing reform would get rid of so-called “three strikes” mandatory life sentences for defendants facing a third drug conviction, except for those with a prior “serious violent felony”, and eliminate “stacking” regulations that make it illegal to posses a firearm while committing a crime, even if the firearm is not used. It would also effectively reduce a slew of federal mandatory minimum sentences by allowing judges to circumvent them for non-violent offenders when they see fit.

The bill would also retroactively extend the 2010 Fair Sentencing Act, a move that could affect thousands of drug offenders serving disproportionately long sentences for crack cocaine versus the powder variant.

Some advocates say the prison reform could release 4,000 people currently serving long sentences, give elderly and terminally ill inmates a path home and invest tens of millions in re-entry programming.