[Vince Ferrer]

which has been with Democrats since the mid-1930s.

I strongly doubt this factoid. The democrats were klansen back then.

[forgotten man]

IIRC Nixon got about half of the black vote in 1960. Condolezza Rice’s father became a Republican because that was the only way he could vote in the South.

[x]

African-Americans didn't have the vote in the Klan-dominated Democrat states back then. In the big Northern cities, they gravitated to FDR and the urban Democratic political machines.

It's true that in the 1930s Blacks were as often to identify with the Republicans as the Democrats and that in the 1950s Eisenhower took a big share of the Black vote, but between 1932 and 1936 the African-American vote flipped from over 70% Republican to over 70% Democrat.

About Trump: if he gets 12% of the Black vote, he'll be doing about as well as Republicans usually do, twice as good as Romney, three times as good as McCain, but I don't see him doing much better than that.