It has happened countless times around the world.
When marital law is delcared, the cops get in line fast becuase they too are looking down the barrel of a gun. It only takes a few examples to be made and the people with uniforms figure out they either play along or get dead or arrested themselves.
There are plenty of angry young men around that will react favorably to a uniform, gun, and paycheck.
It is fun to pretend that you know your local sheriff and he knows you are so you are safe, but the fact is, the last thirty years have been one big exercize in militarizing our police and building a chasm between them and the community.
The formula for fascist police state coups is quite simply and highly effective. It relies on brutality and the softening of the law enforcement group through demonization of other groups.
The last thirty years of demonization of democracts and liberals for instance make it quite easy for right wing police forces to rationalize arresting huge swaths of citizens. That is the benefit of the right's eforts towards dehumanizing other people, be they liberals or Muslims.
Once they are dehumanized, it is easy to kill or arrest them.
Cops, schooled very heavily in law and order" rhetoric, plus post911 fear mongering, will mostly fall in line.
Sure, some will refuse, and some of the cops buddies will be spared a la Anne Frank. But as a rule, we are primed for a fascist style coup. The ground work has been well laid.
My own belief is that the only thing stopping the fascists was that a coup of this sort would ruin the golden goose that is our economy. Er, was.
Unfortunately, now that pirates have carted off large chunks of that, the incentive to keep the peace at home is gone.