The trick here is that US police are absurdly unprofessional in nearly any way. With guns it's even worse, as a mythical "good cop" with a gun gets only a single magazine a year through work to maintain proficiency, and depending on the state requirements, might not even have regular testing of their shooting abilities. Police in the US regularly shoot things that weren't even close to their target, and their standard training is to just keep shooting until they need to reload, whether or not it really makes sense. They are also taught that everything and everyone wants to murder them, and they should shoot first, and that their life is more important than justice, and other things that make them so paranoid they think it's normal to always face the door at a restaurant like my anxiety crippled girlfriend.

Meanwhile plenty of them are in right wing militias.