Who was the first Democratic presidential candidate to sweep the black vote?

Kennedy. Before then, blacks recognized that it was the Democrats who had allowed the KKK and other racist groups to continue and many Democrats, such as Senator Byrd were activly involved in the killing and destruction of Blacks. Somehow, the Democrats convinced the country that they were the party of the minorities and have controlled the minority votes since then. It's interesting that the Republicans have actually appointed blacks to significant positions in the government. It's all about perception. If someone makes a claim enough times, people will eventually start to believe it.