There is a widespread belief that policing in the USA suffers from systemic racism. Let us suppose that Joe Biden gets elected President and decides that this is a priority. Let us also suppose that he can get legislation passed to support his policies.
However, policing in the USA is mostly a local affair. The kind of everyday policing that is at issue here is generally organized at a county or city level. Wikipedia says:
There are 17,985 U.S. police agencies in the United States.
How much influence can the federal executive and legislature have on the way in which local policing is done in the USA?
Edit: In response to comments. The question about "who polices the police" has useful answers; the fact that federal charges can be brought where local oversight fails is important because the executive could easily beef up that aspect of enforcement without any new laws. However I'm also interested in ways in which federal pressure can be bought to bear on systemic problems in recruitment, promotion and general discipline.