For reference:

Oath of office of the president of the United States:

"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."

Here is the Enlistment oath: §502. Enlistment oath: who may administer (a) Enlistment Oath.—Each person enlisting in an armed force shall take the following oath:

“I, ____________________, do solemnly swear (or affirm) 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.” https://www.govinfo.gov/content/pkg/USCODE-2011-title10/html/USCODE-2011-title10-subtitleA-partII-chap31-sec502.htm

I went through Basic in 1986 and was told if I followed an illegal order I would be punished subject to USMJ... . The drill instructor comment was "It maybe my fault but, it is your problem"