President Obama’s use of drones to kill U.S. citizens fighting alongside terrorists is not easily sorted. It puts two constitutional absolutes into conflict — the guarantee of due process to every American, and the obligation to provide for the common defense.

Sometimes it helps to clarify an issue by viewing it in a different historical context, such as this imagined conversation between President Lincoln and Secretary of War Edwin Stanton the day after the Battle of Cold Harbor in June 1864: