RE: Actually, serving in the armed forces of a foreign state actively in conflict with the US, is one of the 7 acts that result in loss of US citizenship. No need for any paperwork, it’s automatic, and unlike treason, does not require a conviction.
Is that a law? Because if so, and if the news that we knew about his whereabouts but our special forces did not engage the enemy to rescue him as a deserter, is true, then we could have just blown away the bastard as an enemy combatant to kingdom come with a drone.