George Lardner Jr., a former Post reporter, is scholar in residence at American University’s Investigative Reporting Project. He is writing a history of the presidential pardon power.

Attorney General Eric H. Holder Jr. has announced plans to reform some of the most disgraceful features of imprisonment on a federal level. But what has his boss, the president of the United States, been doing? The answer, more than four years after President Obama and Holder were sworn in, is: almost nothing.

Holder, at least, is addressing what he acknowledges are “many aspects of our criminal justice system” that make the “vicious cycle of poverty, criminality and incarceration” much worse under the pretense of making it better. The attorney general, as The Post reported, wants to reduce sentences for older, nonviolent inmates and find ways short of prison to deal with nonviolent criminals. He wants federal prosecutors to avoid charges that would impose harsh mandatory sentences on low-level drug offenders. He wants legislation that would give federal judges more leeway in imposing mandatory minimum sentences for various drug offenses, a step that he says would “ultimately save our country billions of dollars.”

Most of those cures are prospective. Holder may not be able to do much on his own for the thousands of prisoners already behind bars because of excessive sentences. Obama, however, could — and without a single word from Congress.

Since 1789, Obama’s office has had the power to “grant reprieves and pardons for offenses against the United States, except in cases of impeachment.” There are no other limits to that power.

More than 210,000 people are behind bars in the federal system, nearly half of them because of drug-related crimes. As Holder said in a speech to the American Bar Association this month, it appears that the sentences imposed on black male offenders are 20 percent harsher than those imposed on white males. “This isn’t just unacceptable,” he said. “It’s shameful.”

Indeed it is. Obama could do something about it without waiting another day. He could start with the thousands of petitions for clemency that typically clog the Justice Department’s understaffed, underfunded Office of the Pardon Attorney. It takes more than three years before those considered deserving are even processed. And while very few are sent to the White House with a positive recommendation, the fact is that Obama has approved even fewer after sitting on them for almost another year.

One petitioner, Drayton Curry, serving a life term for what the Village Voice called “a fairly thin nonviolent drug conspiracy,” died in prison in November at age 92 after waiting almost two years for a response to his clemency request. The candidate who said in 2007 that it was “time we take a hard look at the wisdom of locking up some first-time nonviolent drug users for decades” has become a president who does nothing about people who have been sentenced to prison for life, without the possibility of parole, for nonviolent marijuana offenses.

Last fall, five such individuals asked the president not for pardons, which are usually granted only years after release from prison to restore civil rights, but for commutations that would reduce their mandatory sentences to time served. According to the Pardon Power blog by political scientist P.S. Ruckman Jr., each of the five had been in prison for at least 15 years; each was older than 60; and each “has a stable home environment, job possibility and family awaiting him, if released.” A recent ACLU study found that elderly prisoners cost taxpayers an average of $68,270 a year.

Alexander Hamilton wrote in the Federalist Papers: “The criminal code of every country partakes so much of necessary severity, that without an easy access to exceptions in favor of unfortunate guilt, justice would wear a countenance too sanguinary and cruel.” Hamilton knew giving that power to one person could tempt him to be too forgiving, or too cruel, and end up making him too cautious for fear of criticism, but he argued that “humanity and good policy” would prevail and show “that the benign prerogative of pardoning should be as little as possible fettered or embarrassed.”

So far, Obama has done little to justify Hamilton’s optimism. He has granted just 39 pardons and only one commutation, while denying more than 6,700 petitions. In his first term, Ronald Reagan signed more than 10 times as many pardons and commutations as Obama did (250 vs. 23); George H.W. Bush more than three times as many (77); and Bill Clinton more than twice as many (56). The “easy access” that Hamilton envisioned has nearly disappeared.

In January 2010, Obama said that “one of the great things about America is that we give people second chances.” He could do just that by ordering a special review of the thousands of clemency applications at the Justice Department and White House that are growing older by the day, and by commuting the sentences of offenders of all races that are too severe, like those for the five serving life terms without hope of parole for nonviolent offenses. The Founders gave the president the pardon power for good reason; Obama has not only the right, but also the duty, to use it.