Lewis ‘Scooter’ Libby was pardoned by President Trump last week. (Chip Somodevilla/Getty Images)

Mark Osler is the Robert and Marion Short professor of law at the University of St. Thomas and the author of “Contemporary Criminal Law.”

With his fourth exercise of the clemency power, President Trump has once again chosen to favor someone (Lewis “Scooter” Libby, the chief of staff to former vice president Dick Cheney) who is connected and powerful. Meanwhile, none of the deserving federal prisoners with pending petitions — including many serving narcotics sentences that are now broadly condemned — have received a similar benefit.

This is legal, but it is wrong.

Clemency — which at its best is principled mercy — needs to be considered for those outside the shallow pool of a president’s friends, and friends of friends. Trump’s brutal favoritism makes a mockery of a deeply held principle intentionally placed in the Constitution by the framers.

While few people seem to think federal penalties for perjury, mishandling classified information, fraud and contempt of court are too harsh (at least relative to the many who have criticized the drug laws), they are the offenses committed by those Trump has seen fit for clemency. Libby was convicted of perjury related to the release of a CIA officer’s identity; Kristian Saucier, who was pardoned on March 9, had been convicted of keeping defense information without authorization; Sholom Rubashkin had his sentence for fraud and other crimes commuted on Dec. 20 ; and, perhaps most famously, Joe Arpaio, the former sheriff of Maricopa County, Ariz., was pardoned in August for a conviction on a charge of criminal contempt.

I am not arguing that mercy isn’t a good thing in these cases. In fact, I once signed on to an amicus brief in favor of Rubashkin. Rather, it is disturbing that Trump seems to grant clemency only to those who are connected to him, his friends or Fox News, while thousands of worthy cases linger in the depths of the byzantine clemency process — a system that courses slowly through not only the Office of the Pardon Attorney, but also the offices of the deputy attorney general and the White House counsel.

At its best, though, clemency is used for those who are disfavored and forgotten in a system that, without mercy, “would wear a countenance too sanguinary and cruel,” as Alexander Hamilton put it in No. 74 of the Federalist Papers.

The very first use of clemency, in fact, was granted not to friends of a president, but his enemies: In 1795, President George Washington pardoned some of the leaders of the Whiskey Rebellion, who had been sentenced to death for treason. Notably, Washington had personally led the militias across Pennsylvania to address that insurrection.

Since then, the pardon power has often been deployed to favor not the wealthy and connected, but those who were least popular, including President Abraham Lincoln’s pardons for army deserters and President John F. Kennedy’s quiet clemency grants to those over-sentenced for narcotics.

If Trump wants a template for action, he should look to President Gerald Ford. Yes, Ford granted perhaps the most controversial pardon of all to his predecessor, Richard Nixon. But he also did something really significant in the same month in 1974: He announced a year-long project to grant clemency to Vietnam-era draft evaders and deserters, which offered more than 13,000 conditional pardons.

Trump can, and should, do something similar. Among the more than 11,000 clemency petitions now languishing somewhere in the process are thousands that describe similar stories: narcotics offenders who were over-sentenced, many of whom would receive a much lower sentence under current law. Yes, there are true kingpins in federal prison who deserve to be there. But there are also too many low-level associates, girlfriend-conspirators and small-time dealers.

President Barack Obama attempted to address this issue by targeting factors including nonviolence and low-level involvement to identify the best clemency recipients, but did so inefficiently and left far too many people behind. A survey by the U.S. Sentencing Commission found that “by January 19, 2017, there were 2,687 drug trafficking offenders who had been incarcerated in the Federal Bureau of Prisons when the Clemency Initiative was announced and who appeared to meet all the announced Clemency Initiative factors. Of them, 92 (3.4%) received clemency from President Obama.” A 3.4 percent success rate leaves a lot on the table, Mr. Trump.

The process within the Justice Department is part of the problem, with its redundant layers of bureaucracy. Trump should accomplish what Obama failed to do and revamp that process so that it is shorter, more efficient and more directly connected to him, and then use the pardon power more broadly. One option is to create a clemency board to advise him. Or he could pick a pardon attorney he trusts and have that counselor report directly to him. If he prefers, he could also adopt an idea proposed by Paul Larkin at the Heritage Foundation and assign the clemency evaluation process to the vice president.

Clemency is in the Constitution for a reason, and it is not simply to favor those close to the president. It would be a good time to return to the original, broader purpose.