If he were truly in doubt as to the legitimacy of President Bush's election, I would argue that he would have been duty bound to either satisfy his misgivings regarding the lawfulness of the order, knowingly disobey the order and accept the consequences thereof, or resign his commission.
I'll agree on one and a half of that. First, the half part. satisfy his misgivings just as long he doesn't put the men under his command in danger
Second, resign his commission. I would applaud him for putting integrity over career.
Third, I cannot support him disobeying orders. In doing that he disrupts the chain of command which puts the lives of the men under him at greater risk. It's one thing to turn the other cheek, another to turn another's cheek.