Comment by einpoklum

Also, you swear your oath to defend the _constitution_, against all enemies foreign and _domestic_:

https://www.army.mil/values/oath.html

this comes _before_ the obligation to obey orders. Meaning that, at least in principle, a soldier is obligated to disobey unconstitutional commands, and in fact, to act to countermand them.

Of course that's not what armies are like in practice, but still.