I could write an essay to answer "why," but who has the time?
The key is the "economic justice vs social justice" battle where the Bern has emphasized economic over social and the blacks want social to take presidence. If he had moved to social justice being more important, he could have had them, but he would have lost a lot of his anti-capitalist commie base. So the blacks moved to Billary and O'Madly.
But as far as which one would be better for blacks, the answer is both and neither. Both in that they really only care about them for their votes, and neither in that they are both disinterested about their circumstances equally. Add O'Madly to the mix as he is no different.
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