The marriage debate is entering a new phase. As recently as 1996, a Gallup survey found that 68 percent of Americans opposed civil marriage rights for same-sex couples. On May 8 of this year, Gallup released a report which found that only 48 percent were opposed to same-sex marriage while 50 percent were in favor. The next day, in an interview with Robin Roberts of ABC News, President Barack Obama announced that he too favored the legal recognition of same-sex marriage, a move that delighted social liberals, many of whom believed that the president’s previous tepid opposition was rooted in political concerns rather than real conviction.

Even in the months since, the legal and political ground has continued to shift in favor of same-sex marriage. Just this week, a divided panel of the Second Circuit Court of Appeals ruled that the federal Defense of Marriage Act, a law that limits federal recognition of marriages to couples consisting of one man and one woman, is unconstitutional. Meanwhile, ballot initiatives aiming to uphold laws authorizing same-sex civil marriage are leading in Maine, Maryland and Washington. Perhaps most strikingly, a re-energized Romney campaign has made little effort to capitalize on opposition to same-sex marriage.

Opponents of the practice have no intention of throwing in the towel; nor is it inevitable that the legal and political efforts of advocates will continue to succeed. In November, Sherif Girgis, Robert P. George, and Ryan T. Anderson are releasing What Is Marriage?, a vigorous intellectual critique of the case for same-sex civil marriage that has attracted wide attention in traditionalist circles. Moreover, opponents have achieved a number of political victories at the state and local level, most notably in North Carolina in May of this year.

Yet the deeper problem for opponents, as the political theorist Peter Berkowitz argued in a 2005 Policy Review article on “The Courts, the Constitution, and the Culture of Freedom,” is that what Girgis, George, and Anderson refer to as the conjugal view of marriage, in which procreation and lifelong marital fidelity are central, has been supplanted by a very different view. As Berkowitz put it, “children, once at the center of marriage, have now become negotiable, and what used to be negotiable — love, companionship, sex — has moved to the center.” The legal recognition of same-sex marriage thus represents “an adaptation of law to a profound change in social meaning.”

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In light of this deeper shift, one wonders if we have been having the wrong marriage debate all along. Though no one should discount the importance of the marital aspirations of same-sex couples, it is not the only marriage issue we face. The share of poor and middle-income American adults actually living in stable marriages has been hitting new lows.