That has nothing to do with what I asked. Is the mass incarceration of masses of the black population thanks to policies most championed by Nixon and Reagan more responsible for that plight than mayors? The policy which has deprived massive parts of the population the opportunity of employment, stripped children of their fathers and denied masses of the right to vote? Plus strangely being a policy which because of the all of the last things promotes crime as people have to have money to survive, despite it all.
What about President Clinton's policies? I think you are scapegoating, especially with Reagan. Attitudes toward crime and rehabilitation have changed in general over the course of the last few decades.
Crime can be dealt with in better ways than it was in the past, but it's strange to me that you talk about crime as a main focus considering that it is a symptom of community problems on a local level in many cases.
If you're asking for causal possibilities, consider:
Strengthen the family and reduce crime.
Increase personal responsibility and reduce crime.
Increase employment and reduce crime.
Conversely:
Weaken the family and increase crime.
Decrease personal responsibility and increase crime.
Decrease employment and increase crime.
I could go on.
The Democratic Party has it wrong policy-wise. LBJ wanted to make blacks dependent on the government, and largely he succeeded. More than anything, we see how these Democrat policies, which are arguably rooted in overt white supremacy, served to decimate the black family and black communities to break them apart and make them worse of in measurable terms than they were even in the 1950s, which is shocking but true.
This is without even mentioning the genocidal effects of Planned Parenthood.