WASHINGTON — Anti-Wall Street protesters marched past the gates of the White House on Thursday, bringing their message of economic injustice to the capital and posing an opportunity, but also a threat, to President Obama, who presents himself as a fervent defender of the middle class.

Brandishing placards that said “No More Wall Street White House” and chanting “Shame! Shame!” the crowd took aim at the president, even if it saved most of its vitriol for the nearby headquarters of the U.S. Chamber of Commerce — or as one banner labeled it, “Chamber of Corporate Horrors.”

To hear some Democratic analysts tell it, the mushrooming protests could be the start of a populist movement on the left that counterbalances the surge of the Tea Party on the right, and closes what some Democrats fear is an “enthusiasm gap” between their party and Republicans in the 2012 election.

But that assumes the president is able to win the support of these insurgents, rather than be shunned by them.