From what I understand, listening to other FReepers, it could just mean that the military doesn't have direct arrest powers. They could still investigate, man road blocks, put a bullet through Ackmed's scope.
It's original intent was to get the Yankees out of the South after reconstruction, not to prevent the defense of US soil from foreign invaders or there proxies.
These proxies may very well be American recruits or mercenaries. This wouldn't stop them from being enemy soldiers.
If this isn't just some kid strung out on Ritalin, then this is a War and that changes everything.