Why he did it doesn't matter. If American Blacks are as robotic as the Libs say they are, now they all have to vote for Trump.
Without Blacks, illegals, LGBT, felons, dead people, voter fraud, ballot manipulation, vegans, feminazis, radical Muslims, wall street bankers, and stoned out Communist hippy Liberals, on her side, Hillary has nothing.
Every single person who supports Hillary simultaneously does not support HER, as a person. They are merely supporting themselves and their own special interests through her. Hillary herself as a person is irrelevant to their causes.
These are her core, and only, constituencies. Without this conglomeration of "victim status" subcultures she has no one truely on her side.