I don't know that he lost his base of support so much as the Dems saw him as a huge threat to their African-American base just as they saw Palin as a threat to their female base so practiced similar scorched earth tactics against him. The Dems will do ANYTHING to defeat conservative African-Americans or women to make it look like the GOP and conservatives are nothing more than racist white boys -- look at how much money they poured into defeating Mia Love in Utah.