> They exist to "protect and serve" those in power
While this is technically correct, this phrase sets up a simplistic model of society where there's the Powerful on top, the Police right under them serving them, and the Oppressed under that. I don't think this is the best way to understand what the Police are and what they do.
I've heard many left-leaning people claim something along the lines of "the Police do whatever the Powerful want by taking it out on the Oppressed". This doesn't accurately reflect the behavior or mindset of the individuals who collectively make up the Police. There are thousands of stories of rich and "powerful" individuals being harassed by police officers when their actions or beliefs clashed with the beliefs of the responding officers.
In fact, in America the definition of "power" is almost tautological when it comes to police. You are a "powerful" person when the police will either look the other way or help you when you break the law. I would go as far as to say that in America it is impossible to be "powerful" unless you have the police on your side. (A possible exception is for gang leaders with their own outlaw police forces.) Without the police you do not have meaningful power, and so saying "the police exist to serve the powerful" incorrectly separates the relationship between the "Powerful" and the "Police".
The Police are the power. I like to call them the "Martial Caste", in order to draw connections between them, medieval knights, samurai, cartel sicarios, the KGB, etc. It's all the same thing: they are the muscle behind the societal ownership claims of the local warlords. Without them the warlords are nothing, and without the warlords they are nothing.
A more accurate statement is "the Police exist to protect and serve whatever system perpetuates the Police". If you're a rich and you donate to police causes, suck up to their members, agree with their politics, and generally support police proliferation, they will bend their enforcement tactics to your favor. This makes you "powerful". If you rail against police behavior and try to reform them, they will bend their enforcement tactics against your favor. This makes you "powerless".