From a superb article by Jonathan Chait in the New Republic:
Clintonism, as New America Foundation fellow Mark Schmitt puts it, is a way of accommodating liberalism to a hostile political environment. This is the formative lesson that the Clintons have imbibed. It is also the central view of Hillary's main strategist, Mark Penn, a pollster who came to her via Morris, who has long advocated for moderate policies aimed at affluent, center-right swing voters. It is not an accommodating kind of moderation. It's a moderation that assumes fierce partisan opposition and aims to narrow its target profile and eke out small victories.
No wonder the Clintons disdain Obama's soaring optimism--it flies in the face of all their political experience. Obama's liberal critics depict him marching unarmed into a partisan battlefield. As Paul Krugman has warned in one of his many anti-Obama columns, "[N]othing Mr. Obama has said suggests that he appreciates the bitterness of the battles he will have to fight if he does become president, and tries to get anything done."
Krugman's critique reflects an understandable confusion about Obama's call for unity. In recent years, "bipartisanship" and "national unity" have usually meant meeting the GOP halfway, regardless of how far right it veers, with agreement an end in itself.
But this is not Obama's meaning of national unity. Substantively, he has not embraced many conservative ideas. And he has explicitly repudiated the notion that unity is an end in and of itself--the purpose is to bring in non-Democrats to enact liberal goals. "If you know who you are, if you know what you believe in, if you know what you are fighting for," Obama says, "then you can afford to listen to folks who don't agree with you, you can afford to reach across the aisle every once in a while."
Obama recognizes that polarization is what's preventing Democrats from turning their public opinion advantage into a working majority. His famous 2004 Democratic convention riff about red-staters who "have gay friends" and blue-staters who "worship an awesome God" was not merely a call for unity. It was an attempt to subvert the conservative strategy of cultural divide-and-conquer. Clintonism is a political strategy that assumes a skeptical public; Obamaism is a way of actualizing a latent ideological majority.