The American left is exultant: Expanding civil rights and the retreat of discrimination on race, gender and now sexual orientation mark major milestones for the traditional liberal worldview.

The American left is in mourning: Income inequality has soared to levels not seen since the Gilded Age and the Roaring Twenties, anti-tax orthodoxy is ascendant on the right, the safety net is under attack, and labor unions are barely hanging on.

If the country is becoming more liberal on accepting minority rights, why is the left having such a hard time making progress on its bread-and-butter issues of class and economics, which were once its central, animating concerns? Why is liberalism half-dead, half-alive?

New York’s vote in favor of same-sex marriage captures this peculiar condition. The state that became by far the most populous to legalize gay marriage also is home to the financial industry, which has played a large part in expanding the glaring gap between the ultra-rich and everyone else. Helping push the marriage vote were billionaire financiers who have spent heavily to elect Republicans and block Democratic efforts to regulate Wall Street. And the hero of the vote, Democratic Gov. Andrew Cuomo, has garnered praise from the right for balancing New York’s budget by cutting public education and public employees, instead of raising taxes on millionaires, as liberals preferred that he do.

Some argue that this state of affairs was inevitable — that liberalism in this country has always been most effective when it has aligned itself with ingrained notions of American individualism. Despite notable exceptions, such as Social Security and Medicare, “in general, Americans are more liable to support movements from the left or from the right that talk in terms of rights and individual freedom than talk about collective rights or responsibilities,” said Georgetown University historian Michael Kazin. This extends to the courts, Kazin said, which have lately been more supportive of claims to individual freedoms (say, the right to sell violent video games to kids) than of arguments against big business (see the Supreme Court’s 2010 Citizens United ruling permitting direct corporate spending on elections).

Gay rights advocates say this is the main reason they are seeing a nationwide increase in support for same-sex marriage — because they are seeking simply to affirm the individual freedoms all Americans share. “We’re not trying to take anything away from anybody,” said Fred Sainz, spokesman for the Human Rights Campaign. “Our movement is unique because we’re trying to give people more equality and access. It’s one that’s trying to even the landscape for all. So we insulate ourselves from the attacks on other movements.”

Ken Mehlman, a former Republican Party chairman who is openly gay and was active in the New York lobbying effort, puts it more bluntly. Same-sex marriage is a more successful part of the liberal agenda, he contends, because it’s not necessarily liberal. “This is an issue where there are important conservative arguments for people being treated equally under the law,” he said. “If you believe in maximum freedom and that it’s important to promote strong families and that the golden rule is a good thing to follow, all of those things argue for allowing people to marry the people they love.”

Of course, New Deal-style economic liberals note that polls show even greater public support for liberal planks such as raising taxes on the wealthy than for gay marriage, which recently crept above 50 percent in Gallup’s survey. According to Gallup, 59 percent of Americans say upper-income people pay too little in taxes, and 67 percent say corporations pay too little — which helps explain President Barack Obama’s singling out of tax breaks for billionaires at his news conference this past week. The success of the liberal agenda, from this perspective, is less about where public opinion is than where the money is.

Gay rights proponents in New York had the backing of some very wealthy Wall Street donors who normally support Republican causes but who gave $1 million for the same-sex marriage push, motivated by their libertarian leanings and, in some cases, by the fact that members of their families are gay. When they are not cutting checks for gay marriage, these men are leading the way in opposing higher taxes on the very wealthy and fighting tougher financial regulations, with resources far beyond what organized labor can muster.

Paul Singer of Elliott Management is one of the top Republican donors in the country and head of the conservative Manhattan Institute; Cliff Asness, of AQR Capital Management, has praised the tea party and attended a conference of right-wing donors organized by Charles and David Koch, the bete noires of the left; Daniel Loeb of Third Point and Steven Cohen of SAC Advisors both gave to Obama’s campaign in 2008 but have since turned sharply against him, donating heavily to Republicans. (Spokesmen for all four declined to comment or did not return calls.)

Dennis Poust is a spokesman for the New York State Catholic Conference, which has suffered defeats this year on two fronts: on the same-sex-marriage vote and in state budget discussions, where it tried to prevent cuts to the social safety net, such as aid to the homeless. The gay-marriage cause “has been helped by … very wealthy people who brought in lots of money behind the campaign,” Poust said. “And with the money comes the ability to shape the message, but it also had a dramatic impact on legislators — on their desire to stay in office and the help that kind of money can bring them.”

Sainz, of the Human Rights Campaign, acknowledged the importance of the Wall Street backing but said it was less the money than the signal it sent that same-sex marriage has growing bipartisan support. “Opponents can no longer say, ‘It’s just those wacky liberals,’” he said. He said he knows that the GOP donors are working to undermine other causes of the left, but he expressed no regret. “We do work very closely and in concert with folks in the progressive movement,” he said. “But we also understand there are times when we will have different stakeholders.”

Other left-leaning voices trace the seeming preeminence of issues such as same-sex marriage in the liberal agenda to shifts within the left itself. Writing in the Daily Beast recently, columnist Eric Alterman described “the transition of American liberalism from an ideology focused on the standing of working people to one based on issues of social and cultural freedom that do not interfere with anyone’s ability to make money hand over fist without paying too much of it in taxes.”

John Russo, co-director of the Center for Working-Class Studies at Youngstown State University, says this shift is an unintended consequence of 1970s-era politics. “With the growth of identity politics and multiculturalism,” he said, “class subsided in the attention of the liberals, and as a result of that they were just less attentive to issues of economics.”

Related to this is a theory that the civil rights movement may have hurt public support for social and economic programs, as conservatives sought to cast such efforts as sops to newly empowered racial minorities. It’s a delicate subject for liberals, as it suggests that the two goals of the movement have the potential to undercut each other.

Still, others warn against setting up stark opposition between the liberal fronts. The United States may be unusual in that its partisans generally align on both social and economic issues; in many European countries, socially liberal, economically conservative politicians are common. And for the most part, organized labor in America has been at the forefront of the push for civil rights. Mary Kay Henry, the openly gay president of the Service Employees International Union, said she was inspired by the New York vote — even if it was funded by Wall Street donors who also spend heavily against organized labor.

“The way I think of the [marriage] breakthrough is that it has the same ingredients that we need to make a breakthrough on addressing economic inequality,” she said. “Things that seem impossible to accomplish at one point in time can happen with a lot of individual people standing up.”

Among those cautioning against generalizations is Rep. Barney Frank, an openly gay Massachusetts Democrat whose name is on the financial reform legislation now under attack on Wall Street. He asserts that the liberal shift in public opinion has been unique to gay rights, while conservatives have held their own on social issues such as abortion and immigration. “What you have is a generational shift on LGBT issues. It’s a very specific thing,” he said in an interview. “The number of us who are honest about who we are has reached a critical mass and beaten the prejudice.”

And how does Frank view the gay-marriage push provided by financiers — who will now resume trying to eviscerate the Dodd-Frank law and preserve the loophole that lets their winnings be taxed at only 15 percent?

“I know a couple hedge-fund people helped us on marriage,” he replied without hesitation. “But that’s no reason for me to back off on taxing them.”

Alec MacGillis is a reporter on the national staff of The Washington Post and a co-author of “Landmark: The Inside Story of America’s New Health-Care Law and What It Means for Us All.”