If I sign up, my loyalty is to the country and the Commander in Chief.
"I do solemnly swear that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I will obey the orders of the President of the United States and the orders of the officers appointed over me, according to regulations and the Uniform Code of Military Justice. So help me God."
Note which comes first and which comes last.

The President has already publicly boasted of acts found by the judicial to be a criminal violation of the Constitutional prohibition against unreasonable search and seizure.
So are you going to defend the Constitution by bringing him to justice? Or are you going to obey the President's orders to violate the Geneva Convention?