President Trump on the South Lawn of the White House on May 17. (Jabin Botsford/The Washington Post)

AS MEMORIAL DAY approaches, President Trump has reportedly asked the Justice Department to ready paperwork to pardon several U.S. service members accused or convicted of war crimes, including murder, attempted murder and desecration of a corpse. Each case is distinct, but taken together, such pardons would send a message of disrespect for the laws of war and for the larger values that the United States’ fallen service members have so nobly defended.

War is hell, but there are rules, and the Defense Department maintains a 1,193-page Law of War Manual. The purposes are worth recalling: to protect combatants, noncombatants and civilians from “unnecessary suffering”; provide some basic protections to those who fall into hands of the enemy; facilitate restoration of peace; help commanders ensure the disciplined and efficient use of military forces; and preserve the “professionalism and humanity of combatants.”

Mr. Trump, in pursuit of some hazy notion of military toughness, shows little respect for these principles. On the campaign trail in 2016, he declared that “torture works” and that he would resume the use of waterboarding in interrogations. In 2015, he declared that the families of terrorists should be killed. This month, Mr. Trump signed a full pardon for former Army 1st Lt. Michael Behenna of Oklahoma, who had served in Iraq with the 101st Airborne Division and was convicted of unpremeditated murder. Military intelligence professionals had interrogated a man on suspicion that he was a member of al-Qaeda with knowledge of a roadside bombing in which two U.S. soldiers were killed. They ordered Mr. Behenna to drive the suspect home. He took the detainee to a railroad culvert, stripped him naked, interrogated him at gunpoint and then shot him in the head and chest, saying it was self-defense.

Among those, the New York Times reports that Mr. Trump is now considering for clemency is Special Operations Chief Edward Gallagher of the Navy SEALs, who is scheduled to stand trial soon on charges of shooting unarmed civilians in Iraq and killing an enemy captive with a knife. Others, according to the Times, are believed to include a former Blackwater security contractor, Nicholas A. Slatten, found guilty in the 2007 shooting of dozens of unarmed Iraqis; Maj. Mathew L. Golsteyn, an Army Green Beret charged with killing an unarmed Afghan in 2010; and a group of Marine Corps snipers charged with urinating on dead Taliban fighters.

Pardons in these cases would undermine discipline in the ranks, impede cooperation with citizens and fighters of other nations, and insult millions of service members who have behaved honorably. They would undermine the standing of the United States as a power that believes in — and follows — the rule of law. They would not project strength but rather show weakness, corroding the “professionalism and humanity” of the armed forces.