Oh, b/s. He’s an Islamic jihadist carrying out an act of war against America!
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Yes, but he's also a naturalized U.S. citizen, and Federal law prohibits U.S. citizens from being tried by a military tribunal. There are provisions of Federal law that would allow the govt. to strip his citizenship based on what he's done, but those provisions require proceedings in a Federal court - so, in order to try this guy as an enemy combatant, the govt would essentially first need to try him in court (to strip his citizenship), and only then put him before the military tribunal.