The essence of due process, as Harvard Law professor Noah Feldman recently argued at an Intelligence Squared debate, is that “the government would not kill its own citizens without a trial.” That derived from the English Magna Carta of 1215, and the Framers of the U.S. Constitution had such a history in mind when, in the Fifth Amendment, they wrote that no one may “be deprived of life, liberty, or property, without due process of law.”
So this seems like an easy issue: The Constitution is clear that due process is required before the federal government takes a citizen’s life. But in many cases, that would fly in the face of common sense.
Professor Alan Dershowitz pointed out in the same debate that a bank robber firing at police as he flees is not entitled to a trial before police can shoot back at him. This exception is widened in the case of war, which is why the laws of war have never required a prior hearing before incapacitating an enemy combatant that is on the battlefield.