They vote for him because after the 60's liberal teachers and professors started the meme of how it was the republicans who were for slavery and how the liberals care about them. They fulled them into that regard by giving them all kinds of gifts and keeping them down. If they had a real history class, not one that is watered down to make the Liberals look good, there wouldn't be a single black democrat in this country.
Something else that rings with them is the parties flipped after the 60's. Everyone knows that is a lie, but they of course believe it.