Nobody votes for a political party based on their party platform from 150 years ago.
Good try, but you don't have to go back that far.
Fun facts: Not every Democrat was a member of the KKK ... but every KKK member was a democrat. They had people in congress who were openly racist beyond belief.
They objected to all the civil rights legislation at every point, all of which was eventually passed by republicans.
They are and always have been political opportunists and switched their agenda right at the end, when the writing was on the wall that their position was untenable in the modern world. But they really only changed how they enslave people.
The black electorate doesn't appear to be sophisticated. The same poor thinking and decision making that consistently keeps people poor makes people easy to manipulate politically (these things go together) and coupled with a propensity for group / block voting based on the direction of "community leaders" (who become millionaires in the process) and you have an entire community of people who are perhaps the only voting block that consistently votes against their own self-interests while believing that the people they give their vote to will solve their problems ... any day now, they'll be right on it.
I almost don't even feel sorry for them anymore, but they don't get a chance to learn and think straight because their failing schools are almost wholly run by democrat supporting unions and are really indoctrination centres.
They just changed the definition of "plantation" and people kept picking their cotton as they were told.