President Obama commuted the sentences of 214 federal prisoners on Wednesday. At least 67 of them were serving life sentences, many of those for nonviolent drug crimes.

The White House points out that Obama has granted "more commutations than the previous nine presidents combined and more commutations than any individual president in nearly a century." This is true, but it's also a slightly misleading statistic.

When it comes to granting relief to people convicted of crimes, presidents typically have two options: They can commute a prisoner's sentence or they can pardon the prisoner completely. A commutation "reduces a sentence, either totally or partially, that is then being served, but it does not change the fact of conviction, imply innocence, or remove civil disabilities that apply to the convicted person as a result of the criminal conviction," according to the Justice Department.

A pardon, on the other hand, "is an expression of the president’s forgiveness and ordinarily is granted in recognition of the applicant’s acceptance of responsibility for the crime and established good conduct for a significant period of time after conviction or completion of sentence."

In other words, as legal scholar Michael Walden of New York University once explained, a "pardon wipes out the conviction while a commutation leaves the conviction intact but wipes out the punishment."

Obama has been issuing commutations at a rapid pace in his last few years in office. But he's only issued 70 pardons so far, according to the Justice Department. That's fewer pardons than any president going all the way back to William McKinley, the earliest president for which the Justice Department tracks clemency statistics.

For a fuller picture of presidential clemency actions, it's best to compare the average number of pardons and commutations issued by each president per month of their presidencies. That way, you don't have to worry about different amounts of time in office skewing those numbers.

Here's what that chart looks like for all pardons and commutations, including the latest batch announced by the Obama administration.

At an average of seven pardons or commutations per month, Obama is now issuing clemency actions at a faster pace than any president since Jimmy Carter. But those numbers are still well under historic norms for most of the 20th century. Woodrow Wilson granted pardons and commutations at a rate of nearly 30 per month. Herbert Hoover issued an average of 25 per month.

But the clemency picture under Obama is now very different than it was just two years ago, before Obama's clemency work started in earnest. Back then, he was issuing pardons and commutations at a slower rate than any president of the past century.

The latest commutations are welcome news for criminal justice reform groups, such as Families Against Mandatory Minimums, which are working to reduce overall prison populations. But absent much larger commutation efforts on a massive scale, a single president's efforts aren't likely to make a huge dent in the federal prison population. Obama's 562 commutations and 70 pardons represent approximately one-third of 1 percent of the total federal prison population of 205,000 inmates — to say nothing of the more than 1.3 million people currently held in state prisons.

However, the Obama administration promises its clemency efforts will continue. "Our work is far from finished," White House Counsel Neil Eggleston wrote today. "I expect the president will continue to grant clemency in a historic and inspiring fashion."

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