Over on a thread started this morning, there's some debate over the question of whether the attack executed against Anwar al-Awlaki represents the killing of an American citizen by executive order without due process.
An American citizen who makes the mistake of joining the enemy is not legally inoculated from military attack. What is important is not whether someone is an alien or a citizen, but whether they are a member of an enemy conducting hostilities against the United States. Here are three historical pieces of authority:
1.The Civil War. Every confederate soldier was a U.S. citizen, especially under Lincoln's theory that secession was constitutionally impossible. If one could not kill American citizens who had joined the enemy without some kind of judicial hearing or due process, the Civil War would have been unwinnable.
2. Ex Parte Quirin (1942), where the Supreme Court upheld the detention, trial, and execution of German saboteurs, one of whom was an American citizen. The Supreme Court said: “Citizenship in the United States of an enemy belligerent does not relieve him from the consequences.” One of those consequences, of course, is being subject to attack. In World War II, many Americans returned to Germany, Italy, or Japan to fight on the side of the Axis. The courts never required some kind of due process for them.
3. Hamdi v. Rumsfeld (2004), where the Supreme Court upheld the military detention of a Saudi Arabian caught fighting during the Afghanistan invasion of 2001. The Saudi had happened to be born in Louisiana, but left as an infant. “A citizen, no less than an alien, can be part of or supporting forces hostile to the United States or coalition partners and engaged in an armed conflict against the United States.”