For the police who patrol the street, each city has laws deciding on the qualifications. The only way things will change is if a municipal party senses that they will win or lose an election if they stand on the wrong side of police reform.

State troopers are hired by each individual state, the same principle applies but at another kind of election, probably governor. FBI, CIA, DEA, ICE are federal police, you'd need the democrats or republicans to think they'll lose an election if they don't reform police accountability laws.

Politicians often have many ways to distract the few people who actually vote in American elections, you'd have a better chance if people were more politically mindful, and if more people voted. Complaining for 4 years then voting automatically for the same party every election basically changes nothing, and that;s why they invented wedge politics.