Yup, concerning the monolithic black vote, it's exactly for that reason the dem's have everything to fear. Whereas the gop has hardly any of it, so we don't have to worry about losing any of it, the only place we can go is up. And dem's know this--nothing is forever, and although it'll probably be a long while when it happens, there's no way they can hold on to 90%+ of the black vote forever.
Imagine what would happen to the Rats if their black vote totals went from 90% to 85% ... they'd be sunk