Dean's ideological underpinnings are less evident: Many Democrats say he is the liberal in the field (the White House is certainly trying to) but politicians in Vermont say his record was middle of the road.

If he does not win the Democratic nomination, let alone the presidency, Dean could suffer the fate of McGovern and McCarthy because his appeal is so steeped in the issue of the war.

On the other hand, Dean has the potential to lead an enduring movement because he is less of an establishment figure than those two former senators. There is also a practical advantage that past movement leaders did not have: The Internet could continue to be a backbone of his appeal.

It could be that if Dean does not succeed politically, said Paul Allen Beck, a political scientist at Ohio State University who studies voting behavior and parties, his movement could die with his campaign. "It's very idiosyncratic," he said. "I don't see how anyone else could pick it up right now."

But Frances Fox Piven, a political scientist at the Graduate Center of the City University of New York, has a different view. Piven said Dean's campaign was clever to have adapted for electoral politics the organizing principles of other causes like the global justice movement.

She added that no matter the future of Dean, the movement is already bigger than one person. "What he did was make the movement electoral," Piven said. "If Dean is defeated, the movement will turn away for the time being from electoral politics. But the kind of movement will not go away. It's the way movements now organize: through the Internet."