Same-sex marriage is now unstoppable. For progressives, the U.S. Supreme Court's tossing of the noxious Defense of Marriage Act is a huge win and a rare reason to celebrate. ¶ Now the American left needs to take stock and reassess. Why is it that beyond same-sex marriage the progressive agenda is waning? ¶ There are varied and complex reasons:

• The left is fractured, with environmentalists, civil rights activists, Occupy-movement types, labor supporters, advocates for the poor and their subgroups all working their own agendas.

• It is up against almost unlimited money on the political right from plutocrats like the Koch brothers and corporatists like the U.S. Chamber of Commerce.

• Since President Bill Clinton proclaimed himself a "New Democrat" and pushed aside economic justice issues to give Democrats access to Wall Street money, progressives haven't had a real political home.

But the movement is also, in a sense, suffering from its own success, like an army that took a hill but is now struggling to keep it.

Everywhere you look, there are right-flank attacks.

Texas is poised to ban abortions after 20 weeks and force most abortion clinics in the state to close despite the heroics of state Sen. Wendy Davis' 11-hour filibuster. Over 2011 and 2012, an onslaught of 135 new state laws were passed restricting abortion, according to the Guttmacher Institute.

With preclearance under the Voting Rights Act neutered, Texas, Mississippi, Alabama, South Carolina and Virginia have announced plans to implement or pass strict voter identification requirements or other changes that make it harder for minorities and the poor to vote.

Collective bargaining rights, the very process that created the middle class in America, are under attack anywhere Republicans think they can get away with it. So are public schools, with voucher proponents looking to weaken teachers' unions and proselytize children.

Liberals are tired. How else to explain a U.S. Senate under Democratic control proposing billion-dollar cuts to food stamps and claiming victory because the cuts are not as deep as those wanted by House Republicans?

To inject life back into the progressive movement, it should adjust its zone-defense strategy of parachuting in wherever skirmishes erupt. It should focus more energy on making a sustained, affirmative case for progressive ideas and ideals on an ongoing basis and to the nation as a whole.

Liberals persuaded the nation that same-sex marriage is a net good for society, that children of gays and lesbians should have married parents, that gay and lesbian citizens and taxpayers should be treated equally under the law, and that privacy for intimate relationships should be respected.

There are equally strong, forceful arguments for the proposition that people should earn decent rewards for hard work and have a say on the job; that public education is central to democracy and pluralism; and that women have a right to control their body.

This is what Barry Friedman and Dahlia Lithwick argue in their Slate commentary, "What's Left of the Progressive Cause Other Than Gay Marriage?" They say that progressives in the United States have abandoned, compromised or walked back too much of what they once stood for, scared off by partial-birth abortion, Willie Horton or being perceived as "anti-God." It's time, they say, for the left to embrace a clear agenda and be "for something, not just against the right's most idiotic ideas."

We all know that it is harder to keep up enthusiasm and momentum to protect gains already made. Same-sex marriage is a new right being carved into the grain of a fair society. Abortion rights, public education, due process for criminal suspects and labor rights are already secured — at least in theory — and the job of progressives is to shield them from incursion. Comparatively, it's drudge work.

But we know that none of those vital rights and benefits are as fully realized as they need to be and there has been substantial recent backsliding. Americans are a hungry audience for the progressive case — some literally so. It just has to be aggressively made.