Some of us are not so easily crushed. The moment that anyone tries to use the armed forces against the citizens of the US is when all holy hell will break loose and the would be oppressors will find out just how bad of a mistake they have made.
Tread not upon the serpent for you may find that it is not a snake but the tail of a dragon on which you have stepped.
They don't have to use absolute force everywhere. They would use just enough to squeeze great segments of the population to accepting their actions by fiat. Buy their cars, pay pay their taxes, fly on their planes, watch their media. Go to their doctors, buy their medicines, etc.
They also have no compunction over attacking the very young, very old, and the infirmed. Yes, people can and do eventually regain their freedom. Usually at great cost.