The key in the oath concerning this Marine is “I will obey the orders of the President of the United States”..................................... So I take it that you have accepted the “proven legitimate” President, so ask no questions, just obey? Maybe this marine has doubts, like many others, as to the legitimacy of this presidency? If in fact the President proves to be illegitimate, what then? Gotta see how this plays out.
I think this Marine has more personal problems than we know at the present. War has done this to many military personnel. At times they break and rage takes over. I don’t think this has anything to do with the President.