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.

Back in 2010, the National Marriage Project and the Institute for American Values released a “State of Our Unions” report focused on the uneven retreat from marriage. Among college-educated Americans, who represent 30 percent of the adult population, marriage rates have remained high and marriages have proven to be quite durable. The opposite is true among the 12 percent of Americans without a high school diploma, among whom marriage is rare and quite weak. What the report highlights, however, is the transformation of marriage norms among the 58 percent of the adult population that falls in the “moderately educated” middle of the spectrum, i.e., those with a high school diploma but without a four-year college degree.

By the late 2000s, for example, 6 percent of children born to college-educated women were born outside of marriage. For the least educated mothers, the number was 54 percent. Rather alarmingly, the number was 44 percent among moderately educated mothers. That is, the pattern among the broad middle more closely resembles the pattern among the poorest and most socially isolated Americans than it does the pattern among those at the top.

These numbers wouldn’t be so much of a concern if, as in northern Europe, nonmarital childbearing nevertheless happened in the context of stable relationships. But there has in fact been a marked increase in family disruption. From the 1970s to the 2000s, the share of 14-year-old girls born to moderately educated mothers living with both parents fell from 74 to 58 percent. The share fell from 65 to 52 percent for 14-year-old girls born to the least educated mothers. The only exception to this dismal trend is that 14-year-old girls born to college-educated mothers are slightly more likely to live with both parents — the share increased from 80 to 81 percent in this group. Andrew Cherlin, a sociologist at Johns Hopkins University and author of The Marriage-Go-Round, has referred to “the deinstitutionalization of marriage,” in which marriage has remained a prestigious mark of individual achievement even as adults spend less of their lives in intact marriages. And he has projected, as one of several possible alternatives, a “fading away of marriage” in which marriage continues to lose ground to cohabitation and other less stable arrangements.

A number of thinkers have drawn attention to the decline of marriage. Kay Hymowitz of the Manhattan Institute focused on how diverging marital patterns have exacerbated economic and social inequality in Marriage and Caste in America, and Charles Murray documented the decline of marriage among non-Hispanic white Americans in Coming Apart.

This June, David Blankenhorn, founder of the Institute for American Values, published an op-ed in the New York Times in which he called for a new marriage conversation. Having emerged as one of the leading critics of same-sex civil marriages, which he sees as a potential threat to a fragile institution, Blankenhorn called for a kind of truce. “Instead of fighting gay marriage,” he wrote, “I’d like to help build new coalitions bringing together gays who want to strengthen marriage with straight people who want to do the same.” Earlier this week, Blankenhorn and I discussed the future of the marriage debate and the difficulties of running “a think tank, not a doctrine tank” in a polarized age. Many of Blankenhorn’s erstwhile allies saw his op-ed as a capitulation, and as a result the Institute for American Values lost several members of its board. To be sure, Blankenhorn has gained a number of new allies as well, including Jonathan Rauch, journalist and author of Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America. But the Institute, which has done more to advance the discussion of how marriage contributes to America’s economic and social well-being than institutions many times its size, is at risk of closing its doors within the next six months.

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With rare exceptions, leading politicians have steered clear of this larger marriage conversation. During his campaign for the Republican presidential nomination, Rick Santorum often spoke of how the erosion of married two-parent families contributes to social turmoil, though he did it in a style that alienated potential allies more often than not. President Obama has reflected on the importance of responsible fatherhood, but this hasn’t emerged as one of the themes of his presidency, despite his unique cultural authority on the subject.

Somewhat surprisingly, it was Mitt Romney who, in his own awkward way, injected the issue of family stability into the presidential campaign earlier this week. While ostensibly answering a question about gun violence during this year’s second presidential debate, Romney added, “But gosh, to tell our kids that before they have babies, they ought to think about getting married to someone — that’s a great idea, because if there’s a two-parent family, the prospect of living in poverty goes down dramatically.” Romney was channeling Isabel Sawhill, president of the National Campaign to Prevent Teen Pregnancy and co-director of the Center on Children and Families at the center-left Brookings Institution. Together with her Brookings colleague Ron Haskins, Sawhill has found that adults who finish high school, work full-time, and marry before they have children are less likely to be poor, the numbers falling from 15 percent to 2 percent. Romney has cited this research, which is very much in keeping with his cultural sensibilities, on the campaign trail on numerous occasions.

One obvious rejoinder to Romney is that his prescription for a better life is out of reach for many Americans. This is part of why some on the left, including Richard Kim of The Nation and Lisa Duggan of the University of Pennsylvania, have called for more cultural and economic support for household diversity rather than a focus on marriage. That is, rather than lament the ongoing transformation of American families, Kim and Duggan have argued that we should expand public spending to accommodate the more fluid families of the 21st century.

Another view is that marriage really is uniquely valuable but must be understood in a larger economic context. Sawhill and Haskins have devoted their lives to understanding the challenges facing single mothers, many of whom aspire to marry yet find that the supply of reliable men capable of finding remunerative work is severely limited. Romney, for all his virtues, has spent relatively little time talking about the challenges facing the less educated and even moderately educated men who have seen their economic prospects deteriorate and who have thus become less marriageable than they might have been a generation ago. Indeed, he has spent as little time on this marriage debate as he has on the debate over same-sex marriage.

“Family issues” are often treated as the garnish on the salad of American political debate. But insofar as the core goal of American conservatism is to strengthen civil society and to limit the power of the state, it is worth noting that family instability weakens the capacity for self-reliance, leaving the state to pick up the slack.

PHOTO: Lela McArthur (R) and Stephanie Figarelle, both from Anchorage, AK, kiss on the observation desk of the Empire State Building after being married on the 61st floor in New York, February 14, 2012. REUTERS/Andrew Burton