Mr. McConnell should not delay a vote on a bipartisan deal that took years to strike.

The bill would support programs meant to help federal inmates reintegrate into society after release and expand opportunity for prisoners to earn “good time” credits. Shackling pregnant women would be banned. Mandatory minimum sentences, mainly on drug charges, would be scaled back. Judges would get more leeway to sentence people committed of nonviolent drug crimes to less time than the mandatory minimums prescribe. The bill would end the sentencing disparity between crack and powder cocaine charges — which disproportionately hit African Americans — for some 2,600 federal inmates convicted years ago under this unjust regime. In all, thousands of inmates now and tens of thousands in the future would have a fairer deal.

The bill does not go far enough, but it would be, as its title suggests, a first step. It would apply only to federal inmates, but federal policy can set a tone for the states, which hold most of the nation’s prisoners. Many states in fact have moved first, reforming criminal-justice systems and ending costly and counterproductive get-tough-on-crime laws. A ringing bipartisan endorsement on the federal level would add to the momentum.

Mr. McConnell reportedly fears that considering the act over the next several weeks would eat up time he might rather use on passing a farm bill or confirming conservative judges. There will be plenty of time for the GOP Senate to confirm judges next year. The opportunity to pass this bill might well expire in January, when a new Congress reshapes the policymaking landscape.

Every day that the existing inequitable system goes unreformed extends the unnecessary misery those in U.S. custody must endure. It is past time for change.