What will it take for the left to rally behind Obama again? His Ramadan speech should be a start.

Over the last week, there has been a lot of consternation in the progressive community over White House Press Secretary Robert Gibbs’s interview with The Hill in which he aired a series of grievances with the left. Gibbs offered several caustic comments, perhaps inartfully stated, that captured the White Houses’s frustration with the fact that the president, long-attacked as a socialist by the right, is now also being assailed as a capitulator by the left.

Indeed, some liberals have argued that, on issue after issue, the president has “caved.” These liberals believe that Obama should have fought for a public option, and that he walked away from a winnable fight to get it. Rather than waging war for progressive values, he’s given in.

I completely disagree, and I understand the White House’s concern with the left’s turn against it. On a practical level, liberal angst could do real damage to Democrats this election season by sapping energy from voter turnout efforts. Many progressives, however, don’t seem to realize that this would also harm their cause. After all, won’t a Republican Congress be much, much worse than a Democratic one? (Further food for thought: If the president was the capitulator some on the left accuse him of being, would his actions have spawned the Tea Party that attacks him daily?)

Amid this intensifying friction, Obama staked out a bold, progressive, even unpopular position Friday night when he spoke out in favor of the Islamic center near Ground Zero. “The principle that people of all faiths are welcome in this country and that they will not be treated differently by their government is essential to who we are.  The writ of the founders must endure,” the president said.

The question now is … whither liberals?

Here, we have a moment in which the President has done exactly what the left has been asking him to do—fight for liberal values. He defended the core constitutional right of religious freedom. And, as he did in his famous speech on race in Philadelphia over two years ago, the president spoke last night on behalf of tolerance and against fear.

We know the left can organize on Obama’s behalf: Think tanks like the Center for American Progress (my employer), grassroots groups, advocacy organizations, and a thriving blogosphere helped usher him into the White House. Yet, in the last year, it is the Tea Party that has been demonstrating in the streets, seemingly more able to influence the public mood than the left. This has only hindered progress on important liberal policies and principles. In the wake of Obama’s speech last night, the onus is now on progressives to organize against the coming Republican onslaught from the likes of Sarah Palin and Newt Gingrich—to stand up and say that Obama is right.

The left has demanded fire in the belly from Obama. But will it actually have the president’s back when he shows it? This is a crucial test.

Neera Tanden is the chief operating officer of the Center for American Progress. She served in the Obama and Clinton administrations.