What do you mean? That is exactly what they are trained for, you just do the same thing but even more aggressively. US cops are already pretty aggressive but you can dial that up a lot, they are already trained for this.

Tell the cops that they can shoot anyone looking aggressive and not get questioned and they will happily go out and quell any resistance, don't you think? Tell them they can put people in prison without lawyers getting in their way, that they can torture people to speak without anyone stopping them etc.

US police is very close to a fascist police already so very little has to change. Remember that the US police culture roots came from policing slaves.