HRC, who is essentially a centrist Democrat, is widely perceived as a divisive and polarizing figure. Why so? Because she's a woman, because she's married to Bill, but mostly because for twenty years now, unscrupulous Republicans have been investigating, castigating, and smearing her. Is there a more vilified politician in the world? She's a murderess, a lesbian, an adultery-enabler, a frigid bitch... etc. etc.
Barack Obama is not perceived as a divisive and polarizing figure, but only because Karl Rove and his cruel band of conscienceless propagandists haven't yet gone to work on him. I guarantee that right at this very moment there's a room full of "conservative" operatives who are brainstorming the most vile imaginings about Obama. Think Willie Horton, think swiftboat. They are forging documents, photoshopping pictures; they're developing sick fantasies about Obama's sex life, his wife, his children, his parents, his patriotism, his education, his finances, and certainly, his religion. Don't dare to imagine that racism is dead; the Rovistas will give it new life.
And don't think that you are able to anticipate the attack. It will be disgusting beyond anything that ordinary people are capable of inventing. And it will be cloaked by 527s or disseminated anonymously or leaked.
And then Obama too will become a divisive and polarizing figure.