Members of the military take an oath to the Constitution, not the president.

“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… So help me God.”

So when the president is a “domestic enemy” the constitution comes first. Simple.