Negative campaigning has been around since there have been elections. (And by negative campaigning, I do not mean simply criticizing your opponent. It's perfectly legitimate to criticize your opponent's substantive positions on issues.)
Smears, innuendo and worse has enjoyed a heyday in the past coup,e of decades, however. Some call it Clintonian. Some call it Rovian. Many blame the late Lee Atwater. It's had many fathers and many practitioners and the fact is that it has worked.
But like every marketing technique, it appears to have a shelf-life. And it appears it has expired. Those politicians running the most positive campaigns (Obama, Huckabee and McCain) have done the best. Some running campaigns relying on more negative techniques (Clinton, Romney) have faded.
Being positive is not a guarantee of success, of course. Otherwise Dodd and Biden would have done better. But the media and the public seem to have much less patience for crap like the Obama in Somali garb photo flap. (And is it embarrassing or what that a U.S. Congresswoman could be so ill-informed as to believe that this was Obama in the dress of his "native " country? Geesh! Get a clue, Rep. Stephanie Tubbs Jones! Obama is U.S. born!)
Tonight Hillary will be tempted to go negative on Obama. Good luck on that. If she sticks to substantive criticism, good for her. But if she goes off into silliness expect her campaign to finally collapse.