Once a considerable amount of African Americans begin turning their backs on the Democrats, the dynamics that would evolve are going to be interesting in states like Delaware, Minnesota, or New England.
Why Minnesota and New England?
Because Minnesota and New Hampshire and Maine are quite purplish-blue states.
If Democrats lose support among the AA community, those states may become lost for them.
None of those states are a lock for Democrats, but all three of them are very white. If Democrats do slip with black voters, these are among the last places where such a shift would hurt them.
The states I'd watch would be Georgia, Illinois, Michigan and Pennsylvania, among others.