for example: https://www.justice.gov/opa/pr/justice-department-announces-...
Who is President is very much matters. You clearly see this in the Reagan/Bush/Clinton years, where mass incarceration was in vogue, at the direction of the Attorney General (William Barr), who is part of the executive branch, leading the charge.
I think there's a lot more to it than that. There's also the matter of a lot of war vets becoming police officers, the approach to policing they learned in the military, and their lasting effect on police department culture.