YOu did not understand, so yes, you are missing something.Perhaps I did not phrase this correctly.
If we assume that no racist would vote for a Black man, and observe that 36% voted for Cain (who is Black), then we must logically conclude that if there are racists, they are among the 64% who did NOT vote for Cain.
I would say that this means that somewhere between 0% and 64% of the voters are racists, since none of those who voted for Cain are. (If we assume that no racist would vote for a Black man).
I am not sure that no racist would vote for Cain.Perhaps one might for some ulterior motive. We cannot assume that everyone votes consistent with logic.