The idea that you actually need courts behind you is laughable. Power is enforced through the threat of violence, this is how law enforcement functions. Courts do not have soldiers.
Know who does? Commander-in-Chief, now with full immunity for any official act, like, giving orders to the military.
One could say perhaps the soldiers themselves would be afraid of prosecution and would disobey orders, since they don't get immunity. Until the President pardons them anyway.
Otherwise only one last line of firm defense remains: the oath each serviceman takes to defend the Constitution against all threats, foreign and domestic. That might make someone disobey an illegal order.