It's almost as if the cross-tabs in national and state polls overestimate Black support for the GOP every cycle but when polls are done exclusively among Black voters it shows them pretty much in line with prior cycles. Imagine that. Now we wait for Nate Cohn to write about this poll and why it diverges from them so much. 

Harris' issue isn't support among Black voters, it's getting them to come out, particularly Black men (Black women almost always turnout in large numbers).