Leftists are binary in their in thinking: they either love you or hate you. If they no longer "Strongly Approve" of the Liberal Messiah, they will "Strongly Disapprove" of Him. Imagine His "Approval Index" at that point.
Figure that the black vote gives him a floor of 10-12%.
Add in the liberal moonbats, the people who always vote Dem because their great-great-grandpappy did, and the people who won't (or just can't) admit to making a mistake with BO, and you're somewhere around 20-25%. Which, I think, is the number that BO is approaching right now.