http://usmilitary.about.com/od/punitivearticles/a/mcm94.htm
“(b) Mutiny by refusing to obey orders or perform duties. Mutiny by refusing to obey orders or perform duties requires collective insubordination and necessarily includes some combination of two or more persons in resisting lawful military authority. This concert of insubordination need not be preconceived, nor is it necessary that the insubordination be active or violent. It may consist simply of a persistent and concerted refusal or omission to obey orders, or to do duty, with an insubordinate intent, that is, with an intent to usurp or override lawful military authority. The intent may be declared in words or inferred from acts, omissions, or surrounding circumstances.”
There needs to be two important intentions by the mutineer.
1)..it must be concerted and persistent in disobeying orders...a one time walk out due to perceived unconstitutional actions by the government wouldn’t meet the definition of persistent.
2) “an intent to usurp or override lawful military authority.” There is no intent by the act described to actually usurp or override lawful military authority. In fact the clear intent of the described act would be to conform government policy to “lawful military authority.”
The intent is not to usurp military authority but to enforce proper Constitutional authority and the act of defiance is not persistent.
A key point is that, in general, the US military is apolitical. It is a fundamental aspect of what makes our armed forces great. Ive served with officers from other countries who cannot get their heads around the fact that (1) our people can vote for whomever they wish without command interference and (2) that the military has no control, direct or indirect, over elections. In the hypothetical presented I believe the action contemplated would meet the legal definition of mutiny. As a commander I would hammer them without mercy, but would likely not prefer charges of mutiny for the first attempt.