Legal options? Legal options laid down by the regime perpetrating the terror in question? There's a certain amount of irony there.
He was a paid employee of the United States Armed Forces, and he joined as per his wish. No one forced him to join the USAF. But once you join the USAF, you have to abide by the laws and regulations, which are outlined by it. If he was against the war in Afghanistan, then he had a better option of staying at home, doing some other job.