From Robert Levy:
The administration argues that suspected al Qaida terrorists – even U.S. citizens – can be targeted for assassination because they either (a) pose an imminent threat or (b) are part of an enemy army; and (c) other governments are unwilling or unable to act. Although the Fifth Amendment ensures that persons not be denied due process, it’s unclear what process is “due” – especially when the person is a citizen. For example, a U.S. citizen who threatens hostages with imminent loss of life can be killed by law enforcement authorities. Similarly, an American who serves in a foreign army against which the United States is at war is plainly a legitimate target.
Moreover, under the Nationality Act, a citizen can lose his citizenship if he intends to do so (although intent can be inferred by actions) and he either (a) declares allegiance to a foreign state, (b) serves in a post requiring such a declaration, (c) serves in armed forces in combat with the United States, or (d) serves as an officer or NCO in the armed forces of a foreign state.
Still, the killing of Awlaki is a close legal call. On balance, it’s probably unlawful. The imminent-threat contention isn’t credible. To my knowledge, no one has identified a threat that is imminent (meaning: about to happen). The part-of-an-enemy-army claim and the loss-of-citizenship argument raise several questions: First, is the Nationality Act itself constitutional? The Constitution establishes criteria for citizenship. Stripping someone of citizenship effectively changes those criteria, and Congress may not have that power. Second, even if the Nationality Act is constitutional, does al Qaida qualify as a foreign state for purposes of the Act? Are al Qaida agents equivalent to soldiers engaged in combat with the United States? Third, even if the Nationality Act might apply in Awlaki’s case, how do we know that he triggered the provisions of the Act? Can the administration simply assert that he met one of the tests for loss of citizenship, or must there be some threshold process to make that determination?
Finally, the Authorization for the Use of Military Force sanctioned force against those involved in the 9/11 tragedy. Awlaki, although not directly involved, probably qualified as part of an “associated force”; but actions that might self-evidently be lawful if Awlaki were actively fighting on a battlefield are less so when he’s allegedly plotting attacks from Yemen.