“These movements have the potential to reignite the progressive spark needed to address some of the nation’s biggest problems,” the center declared in one Web posting.

But while some Democrats see the movement as providing a political boost, the party’s alignment with the eclectic mix of protesters makes others nervous. They see the prospect of the protesters pushing the party dangerously to the left — just as the Tea Party has often pushed Republicans further to the right and made for intraparty run-ins…

“That’s the danger with something like this — that you go from peaceful protests to throwing trash cans,” said a senior House Democratic official, who spoke on condition of anonymity…

Matt Bennett, vice president for Third Way, a Democratic think tank in Washington that favors a more centrist approach, said he believes the angry and sometimes radical tone of the protests may turn off moderate swing voters who will be critical in the 2012 elections, just as many moderates are put off by the rhetoric of the Tea Party on the right.

Embracing the protests may prove a mistake for Democrats, Mr. Bennett said. “There’s not much upside,” he said, “and there’s a lot of downside.”