In a 2010 Fox News interview, under pressure to explain whether the Obama administration was any closer to capturing or killing Osama bin Laden, Mr. Kerry’s predecessor, Hillary Rodham Clinton, said that “we have gotten closer because we have been able to kill a number of their trainers, their operational people, their financiers.” That revelation — killing financiers — appears not to have been noticed very widely.

As I have written, sweeping financiers into the group of people who can be killed in armed conflict stretches the laws of war beyond recognition. But this is not the only stretch the Obama administration seems to have made. The administration still hasn’t disavowed its stance, disclosed last May in a New York Times article, that military-age males killed in a strike zone are counted as combatants absent explicit posthumous evidence proving otherwise.

Mr. Holder’s one-word answer — “no” — is not a step toward the greater transparency that President Obama pledged when he came into office, but has not delivered, in the realm of national security.

By declining to specify what it means to be “engaged in combat,” the letter does not foreclose the possible scenario — however hypothetical — of a military drone strike, against a United States citizen, on American soil. It also raises anew questions about the standards the administration has used in deciding to use drone strikes to kill Americans suspected of terrorist involvement overseas — notably Anwar al-Awlaki, the American-born cleric who was killed in a drone strike in Yemen in 2011.

Is there any reason to believe that military drones will soon be hovering over Manhattan, aiming to kill Americans believed to be involved in terrorist financing? No.

But is it well past time for the United States government to specify, precisely, its views on whom it thinks it can kill in the struggle against Al Qaeda and other terrorist forces? The answer is yes.

The Obama administration’s continued refusal to do so should alarm any American concerned about the constitutional right of our citizens — no matter what evil they may or may not be engaged in — to due process under the law. For those Americans, Mr. Holder’s seemingly simple but maddeningly vague letter offers no reassurance.