In the US, the police force is locally raised and what training they receive at the police academy is short and poor. There is no attempt to form them into an anonymous "arm of the law", they are just locals enforcing local mores. If the people would approve of the sheriff jailing a black teenager by mistaking the birdshit on his car for cocaine (https://www.vice.com/en_us/article/zmj9gx/nothings-happening...), the cops will do just that.

That would explain why even when people distrust the government they approve of the police, simply because they are not the government from far away imposing an alien law, they are the local posse keeping order.