President Obama. (Jacquelyn Martin/Associated Press)

PRESIDENT OBAMA began August by commuting the sentences of 214 federal inmates, and he ended the month by commuting 111 more. Generally the pardon and commutation power is used sparingly and gets attention only when presidents use it to help cronies or former staffers. Now it is being used to commute the sentences of people who could not spare a dime to donate to a political campaign. This is a historic milestone — but it is also not nearly enough.

Mr. Obama’s August tally is the highest one-month presidential commutation total ever — even including those last-minute flurries of commutations and pardons presidents typically unleash during their final days in office. In a single month, Mr. Obama doubled the number of sentences he has shortened since taking office — to 673. His accelerating pace reflects an initiative to use the commutation power with more ambition than any modern president. His cumulative total is higher than that of the past 10 presidents combined.

The president has the power to shorten sentences in order to compensate for inequities in the justice system, an authority and responsibility that most neglect. Two years ago, the Obama Justice Department announced a program to encourage certain types of federal prisoners to petition for clemency. Mr. Obama chose to target inmates who are serving long sentences for nonviolent crimes, mostly drug-related, and who would be sentenced more leniently under current rules. The White House points out that more than a third of those the president has commuted were serving life sentences, even though they were relatively low-level offenders.

If society has determined that old sentences were too harsh for the crimes they were meant to punish, the interests of justice and good sense are served by reducing the sentences of those who have paid their debt. Over-incarcerating people is not just inhumane; it is also expensive. And, though crime has undoubtedly dropped over the past several decades during which many people were locked up, prioritizing the least threatening of inmates for early release makes the clemency initiative unlikely to harm public safety.

Yet even applying this principle is a massive undertaking. The announcement of the Justice Department’s 2014 commutation initiative led to a huge increase in the number of petitions submitted. At the start of fiscal 2016, 9,115 commutation petitions were pending. Since then, 8,843 more have come in. As of the end of August, the Obama administration had closed 5,694 cases this year. Not all — probably not even close to a majority — of the prisoners who apply for clemency will fit the Justice Department’s criteria. The Clemency Project, an umbrella organization for nonprofits working to prepare clemency applications, reports that it has submitted about 1,700 petitions that jibe with the Obama administration’s criteria.

The Justice Department claims it can review every drug petition that has been submitted before Mr. Obama leaves office. The administration should be held to that promise. It should also remain open to petitions from non-drug offenders who, because of the clemency initiative, sent in applications. There may be some deserving files in that batch, too.