In a speech to law-enforcement officers on Long Island, in 2017, President Trump offered advice about how arrestees should be treated. “When you see these thugs being thrown into the back of a paddy wagon—you just see them thrown in, rough—I said, ‘Please don’t be too nice,’ ” he said. “When you guys put somebody in the car and you’re protecting their head, you know, the way you put their hand over? Like, don’t hit their head—and they’ve just killed somebody—don’t hit their head? I said you can take the hand away, O.K.?”

Nearly a year and a half later, Trump—who never recanted his support for executing the now-exonerated Central Park Five—is backing one of the most significant criminal-justice-reform bills in decades, a bipartisan effort called the First Step Act, which is expected to come to a vote in the Senate this week. “We’re all better off when former inmates can receive and reënter society as law-abiding, productive citizens,” Trump said in remarks endorsing the bill last month. “And, thanks to our booming economy, they now have a chance at more opportunities than they’ve ever had before.”

That the bill has advanced this far under the Trump Administration reflects the purchase criminal-justice reform has gained not only among Democrats but also among conservative Republicans. The bill’s list of supporters includes Ted Cruz and Kirsten Gillibrand, the Koch brothers and the American Civil Liberties Union. The significant buy-in from the right is the culmination of years of effort from a cadre of libertarian-leaning conservatives, like the anti-tax zealot Grover Norquist, and evangelicals, such as Chuck Colson, the founder of the Christian nonprofit organization Prison Fellowship, who have worked to convince others that the prison system has become too costly, punitive, and government-empowering.

Most of their successes have come at the state level, in places like Georgia and Texas, where Republicans have worked to reduce the incarceration of nonviolent offenders and boost anti-recidivism efforts. In Georgia, the incarceration rate for black males has declined by thirty per cent over the past eight years, and recidivism rates for those who complete vocational training or a G.E.D. while imprisoned have also dropped sharply—which the outgoing Republican governor Nathan Deal notes happened under his tenure.

In a piece for National Review, published in late November, Senator Mike Lee, a Republican from Utah and one of the First Step Act’s leading advocates, neatly made the conservative case for the bill and for federal-level criminal-justice reform. “Unlike some reformers, I don’t think our justice system is fundamentally broken, unjust, or corrupt,” Lee wrote. “I know from experience that dangerous criminals exist—individuals who are incapable of or uninterested in rehabilitation and change. . . . But my time as a prosecutor also tells me that not every criminal is dangerous or incapable of living a productive life,” he wrote. “My faith as a Christian teaches me that many people are capable of redemption. And my instincts as a conservative make me believe that the government can be reformed to work better.”

The act’s major reforms include making the 2010 Fair Sentencing Act’s reduction in the disparities between sentences for crack and powdered cocaine retroactive, granting judges more freedom from mandatory-minimum sentences, and expanding the time credits that prisoners can earn and put toward reducing their sentences or qualifying for release into transitional programs. The bill’s supporters estimate that as many as four thousand prisoners could immediately qualify for early release once the bill takes effect.

There are loud dissenters within Republican ranks, led by Senator Tom Cotton, of Arkansas, a conservative hard-liner fond of scuttling bipartisan legislation. One point of contention is how the bill applies to those with fentanyl-related convictions. “Last year, 72,000 Americans died from drug overdoses,” Cotton tweeted, in late November. “Why does the bill reduce the penalty for repeat fentanyl and heroin traffickers?”

Cotton’s objections have frustrated conservative advocates of the bill, including Derek Cohen, the director of Right on Crime, a criminal-justice-reform group backed by the Koch brothers. “I definitely don’t believe his heart isn’t in the right place,” Cohen said of Cotton. “I do think there is some willful obtuseness, when it comes to the First Step Act, on the part of him and some other senators, just in the language they use when they’re talking about the bill itself.” Cotton’s claims about fentanyl convicts, Cohen said, were one example. “It explicitly says in the bill that fentanyl traffickers are exempted from the earned-credit system,” he said.

The bill has since been revised to address concerns raised by Cotton and others. It now makes a larger set of prisoners ineligible for time credits, including low-level fentanyl offenders. (Previously, the bill forbade credits for those “who were organizers, leaders, managers, or supervisors.”) It also excludes those convicted of assaulting law-enforcement officers with a deadly weapon, trafficking undocumented immigrants with histories of aggravated felonies, and committing felonies while affiliated with a street gang. Cotton and Kennedy are expected to attempt further amending to the bill with provisions restricting the number of convicts who might qualify for reduced sentences, a move that might erode support for the bill among Senate Democrats.

If Cotton and Kennedy are defeated, the bill seems likely to pass with the support of Senate Democrats and a sizable proportion of Senate Republicans. That may well be because the First Step Act is ultimately a very modest step in the direction of addressing mass incarceration. Federal prisons, to which the act applies, hold just over a hundred and eighty thousand of America’s more than two million inmates. Kara Gotsch, the director of strategic initiatives for the liberal reform group the Sentencing Project, which supports the bill, told me, “I get somewhat frustrated when I hear supporters of the bill call it transformational change, because it’s not. It’s progress. I think we have a long way to go, and a lot bigger reforms and investment of resources need to happen before we get to a transformation.”

Gotsch argued that the impact of the act’s reforms could be limited, even at the federal level, given the authority that the executive branch would have in administering and implementing its provisions. “It’s about having a President who is willing to talk about these issues and prioritize them,” she said. “I’ve worked with Democratic Congresses before, and if the President wasn’t championing criminal-justice reform they were not prioritizing it. So who sits in the White House and who the Attorney General is is really important.”

Under Jeff Sessions, the Justice Department’s Bureau of Prisons curbed admissions to halfway houses and dismissed an Obama appointee tasked with reforming education within the federal prison system. It seems safe to say, moreover, that Trump isn’t backing the act out of deep empathy for federal convicts. He made his speech endorsing the bill just over a week after Republicans lost the House in this year’s midterms, winning him, for a short window of time, a palliative positive headline.

Some of the strongest advocates for the bill and conservative reform seem to be those with personal connections to the criminal-justice system. Much of the public and private heavy lifting in building support for the bill has been done by Jared Kushner, who made a rare appearance on Sean Hannity’s show to promote it and is reportedly responsible for securing an endorsement of the bill from Fox News. Kushner’s father, Charles Kushner, spent over a year in federal prison after being convicted for white-collar crimes, in 2005.

The Koch brothers are major backers of the bill and the conservative shift on criminal justice. Their company was prosecuted, in 2000, for hiding emissions of the carcinogen benzene at a Texas refinery from government regulators. (They settled.) In a 2016 piece for The New Yorker, Jane Mayer spoke with the Koch Industries general counsel Mark Holden, who described the prosecution as a “a huge overreach, a grave injustice” that had spurred the Kochs to action. “We were very skeptical, going forward, of criminal prosecutors having too much power,” he said. “So we got involved in criminal-justice reform.”

In the summer of 2016, bipartisan efforts at criminal-justice reform foundered, in part because of Republican support for requiring prosecutors to prove criminal intent for offenses lacking an intent standard, potentially including corporate crimes. In a recent National Review piece, Cotton proposed this as one of the reforms conservatives should be pursuing instead of the First Step Act’s initiatives. They likely won’t get a chance to do so anytime soon—Democrats, who will have control of the House in the new Congress, roundly rejected those proposals the last time around.