Killing is not like torture. Torture is never justified, even in wartime. But killing is an integral, if unfortunate, aspect of war. Targeted killing is therefore not inherently illegal; after all, it beats the tragically untargeted killing used in the World War II bombings of Dresden, London and Hiroshima.
Nor is it always forbidden to kill an American. If a U.S. citizen were fighting alongside al-Qaeda on an Afghan battlefield, would anyone question the right of U.S. troops to shoot and kill him? And President Abraham Lincoln violated no constitutional guarantee by authorizing Union troops to fire on American citizens fighting for the Confederacy.
The government can also legally kill Americans in some non-wartime circumstances. The Supreme Court has held, for example, that the Fourth Amendment permits a police officer to use deadly force against a fleeing felon if the felon poses “a significant threat of death or serious physical injury to the officer or others.” The FBI team that on Monday killed an Alabama man who had held a 5-year-old boy hostage for nearly a week certainly did not act unconstitutionally.
But since when is it constitutional for the president to deliberately kill an American while refusing to admit that he has done so? Due process forbids the taking of life or liberty without fair procedures and prohibits any official action that “shocks the conscience,” as the Supreme Court has stated. If secret killing does not shock the conscience, then nothing does.