It’s always been pretty easy to get politicians to pass new laws to create new crimes or to send people to prison for longer periods of time for existing crimes. But, as the New York Times explained in an editorial over the weekend, getting them to rescind laws or ease up on draconian penalties is a much tougher task.

Two bills, each with Republican and Democratic sponsors, were expected to come up for a vote by this summer — one that would reduce lengthy sentences for many low-level drug offenders and another that would give low-risk inmates credit toward early release if they participate in job-training and drug treatment programs. But progress on both bills has stalled, and congressional leaders who were once confident about their chances this year are now looking toward 2015, at the earliest.

Meanwhile, tens of thousands of federal inmates — many of whom have already served years of unjustly long drug sentences — continue to sit in overstuffed prisons, wasting both their lives and taxpayer dollars at no demonstrable benefit to public safety.

The slowdown is all the more frustrating because there is mounting evidence that criminal justice reform works. States from South Carolina to Ohio to Rhode Island have cut back on mandatory minimums, improved rehabilitation services and reduced their prison populations while seeing crime rates go down, or at least not go up.

So why the delay? One major factor has been resistance from members of the old guard, who refuse to let go of their tough-on-crime mind-set. In May, three senior Republican senators — Charles Grassley of Iowa, John Cornyn of Texas and Jeff Sessions of Alabama — came out against the sentencing reductions, arguing that mandatory minimums are only used for the highest-level drug traffickers. This assertion is contradicted by data from the United States Sentencing Commission, which found that 40 percent of federal drug defendants were couriers or low-level dealers.

Another factor was the Obama administration’s April announcement that it would consider clemency for hundreds, if not thousands, of inmates currently serving time under older, harsher drug laws. Republicans complained that this — along with other executive actions on criminal justice by Mr. Obama and Attorney General Eric Holder Jr. — took the wind out of reform’s sails.

The old-guard Republicans were only really a minor barrier. There had been a consensus to move these bills along. It was the Obama administration’s perfectly constitutional plan to grant clemency that seems to have held up reform. Republicans claim it is an executive power grab, which, as I’ve written before here at The Watch, is rather preposterous, given that the clemency power is expressly granted in the Constitution and that GOP leaders have found little reason to oppose expansions of executive power  far more constitutionally suspect, including war-making, indefinite detention, assassination and a host of other issues related (sometimes only vaguely) to national security. A more cynical explanation for the holdup could be that the GOP just doesn’t want Obama to get credit for sentencing reform.

Whatever the motivation, this much seems clear: The Republicans’ new obstinacy has far more to do with politics than with sentencing reform.