Still, what may prove more significant, as Democrats begin to focus on the choice ahead of them and attention shifts from the Republican contest after last week’s debate, are the ways in which the two liberals from Vermont are different.

For Mr. Dean, a defining issue was his opposition to the war in Iraq as he seized on the overriding concern of many Democratic primary voters to distinguish himself from Mr. Edwards and Mr. Kerry. By contrast, Mr. Sanders can speak for 60 minutes without once mentioning foreign policy; his animating issues are economic inequality and the corrupting influence of money in politics.

Mr. Dean was, at 55, a kinetic live wire of a candidate, plunging into his first national campaign after 22 years in Vermont politics. Mr. Sanders, 73, is, at least in comparison, the measured if stern family uncle, an independent who for all his association with the progressive politics of Burlington shows the command of policy that comes with being a product of Washington, where he has served since 1991.

Mr. Dean was wary of people who tried to paint him as being too far to the left. Mr. Sanders is a self-described socialist, and that political philosophy is celebrated in campaign speeches that, while in some ways reminiscent of Mr. Dean’s appeals, seem to take them one step further. “The only way we are going to transform America is to develop a strong grass-roots movement that I call a revolution,” he told members of Netroots Nation, an organization of liberal activists, at its convention in Phoenix in July. “We need a mass movement of the American people to say enough is enough.”

And in an age of unforgiving news and social media, Mr. Sanders has so far displayed a discipline on the campaign trail that often eluded Mr. Dean. The former governor was prone, in all his exuberance, to self-destructive missteps and bursts of anger. He had to apologize for asserting that Mr. Edwards had been deceptive about voting for the Iraq war resolution (he had not), then apologize again after coming under fire from his rivals for declaring that he wanted to be the “the candidate for guys with Confederate flags in their pickup trucks.”

Mr. Dean’s campaign was undone, as much as anything, by the release of videotapes of public television appearances in Vermont in which he had disparaged the Iowa caucuses.