Jurisdiction....... cops, sheriffs, highway patrol...state police......fbi....are all seperate entitys and all can arrest each other if the offending party is in the arresting partys jurisdiction.
A city cop can arrest an fbi agent or a secret service agent or a treasury department agent or even a cia agent if he has a reason to do.
And as far as city cops leaning one way or the other politically...... Id say that when a city hires a police chief......they sort of know how he leans and they probably take how he leans and how they lean into consideration when hiring them.
The last couple of police chiefs in my town were the second in commands who were just promoted to chief. Back in the 80s the city did a nationwide search for a chief and ended up hiring a pervert out of sitka alaska...... after that fiasco they just started promoting folks who they knew were decent people.
Of course they didnt get rid of him cause of sexual allegations involving an underaged girl..... that story hit our papers and the city and the chief just decided to part ways.......lol