But Mr. Grassley, for reasons that defy basic fairness and empirical data, has remained an opponent of almost any reduction of those sentences. In a speech from the Senate floor this month, he called the bills “lenient and, frankly, dangerous,” and he raised the specter of high-level drug traffickers spilling onto the streets.

Mr. Grassley is as mistaken as he is powerful. Mandatory minimums have, in fact, been used to punish many lower-level offenders who were not their intended targets. Meanwhile, the persistent fantasy that locking up more people leads to less crime continues to be debunked. States from California to New York to Texas have reduced prison populations and crime rates at the same time. A report released last week by the Brennan Center for Justice found that since 2000 putting more people behind bars has had essentially no effect on the national crime rate.

The bill that appears to have the best chance of passing anytime soon is known as the Corrections Act — that’s actually a sprawling acronym for Corrections Oversight, Recidivism Reduction, and Eliminating Costs for Taxpayers in Our National System. Co-sponsored by Senator John Cornyn, Republican of Texas, and Senator Sheldon Whitehouse, Democrat of Rhode Island, the bill’s name is more ambitious than its goals, which include giving a narrow group of inmates the chance to participate in educational and other programs in exchange for earlier release. (The bill authorizes no financing for these programs, relying instead on, among other things, the volunteer efforts of faith-based groups.)

Rehabilitation is a laudable aim, and it should be a part of any sentencing reform package. But the Cornyn-Whitehouse bill would exclude nearly half of all federal prisoners — in many cases without any evidence that they pose a greater risk to public safety.

The bill also relies on an inmate’s criminal history. This is a legitimate measure when it is used with the awareness that law enforcement disproportionately targets minorities. The danger is that white-collar prisoners, who are most often white, will receive the law’s benefits, while, say, drug offenders, who are disproportionately African-American, will be left out. Finally, the bill pushes the use of data-based risk-assessment tools, which sound smart but again — because they rely on factors like a person’s employment history, neighborhood and education level — often have racially disproportionate effects.