Via Michael Cohen, here’s the part of Article 88 of the Uniform Code which deals with insubordination:

Any commissioned officer who uses contemptuous words against the President, the Vice President, Congress, the Secretary of Defense, the Secretary of a military department, the Secretary of Transportation, or the Governor or legislature of any State, Territory, Commonwealth, or possession in which he is on duty or present shall be punished as a court-martial may direct.

Americans are fond of quoting John Adams’ description of their country as “a nation of laws, not of men.” So when do the courts-martial start?
UPDATE: I was just reminded of Truman’s wonderful assessment of MacArthur:

I fired him because he wouldn’t respect the authority of the President. I didn’t fire him because he was a dumb son of a bitch, although he was, but that’s not against the law for generals. If it was, half to three-quarters of them would be in jail.