On gay marriage, the U.S. has turned onto the road not taken on abortion.

Through the early 1970s, states went their separate ways on abortion, with some legalizing it and others reaffirming long-standing bans. The nation, for better or worse, appeared headed for a patchwork of laws that reflected the political balance in the different states—until the Supreme Court preempted the process in 1973 by establishing a national right to abortion in its landmark Roe v. Wade decision.

Ever since, some analysts have questioned whether abortion would have provoked less division if the Court had allowed states to ban or permit it, based on local attitudes. Gay marriage now presents a chance to conduct that experiment. With gay-marriage advocates achieving breakthroughs in socially liberal places such as Washington state and Maryland, America is hurtling toward a cultural partitioning in which gay marriage (or civil unions) is increasingly common in Democratic-leaning states while remaining taboo in Republican-leaning states. Because neither the Supreme Court nor Congress seems poised to short-circuit this sorting out with a national resolution, the U.S. is about to test whether it can avoid the intense polarization that followed Roe if states remain free, at least temporarily, to set contrasting standards on gay unions.

The Roe decision followed a period of accelerating agitation in the states. In the years before the ruling, Alaska, Hawaii, New York, and Washington completely repealed their statutes banning abortion. Another 13 states loosened their restrictions to allow abortions in cases where physicians determined that pregnancy threatened a woman’s physical or mental health, or if it resulted from rape or incest.

But while the momentum was toward liberalizing abortion laws, opposition had not crumbled. In the states that loosened but did not eliminate their restrictions, women still often faced arduous tests to prove that a pregnancy threatened their health. A nascent right-to-life movement mobilized to defend the remaining state prohibitions—and to overturn some of the reforms. Gallup polls showed an uptick in support for legalized abortion from 1969 through 1972, but “it is not evident that a majority (or even a plurality) supported the pro-choice position by 1973,” wrote University of Maryland government professor Eric Uslaner and a colleague in a 1979 study.

Although the Roe decision ended the immediate legislative skirmishing over abortion, it escalated the war. Before the decision, both conservative- and liberal-leaning states had loosened restrictions. After the decision, opinion over abortion polarized much more along ideological, partisan, and religious lines. “The divisions … came after the Supreme Court ruled,” Uslaner says. In retrospect, the Court acted before a national consensus had emerged.

Gay-marriage advocates today are gaining ground faster than abortion-rights supporters did before Roe. Last year, Gallup found that 53 percent of adults supported same-sex marriage, double the share in 1996. More than two-thirds of Democrats and nearly three-fifths of independents backed gay unions, as did 70 percent of young adults. Clyde Wilcox, a Georgetown University political scientist who studies culture and politics, says that “this has been the single most rapid change in public opinion” he has ever seen on a social issue.

Propelled by those changing attitudes, Democratic-leaning states have moved steadily to allow such unions since the Massachusetts Supreme Court set the precedent in 2003 by ruling that the state constitution guaranteed same-sex couples the right to marry. After New York acted last year, Washington this month became the seventh state to authorize gay marriage, and Maryland may follow soon. Only a veto by Republican Gov. Chris Christie prevented New Jersey from concurring. In all, 11 of the 18 “blue wall” states that have voted Democratic in at least the past five presidential elections have authorized gay marriage or civil unions; Maine (via referendum) and California (by court ruling) could join them this year. New Hampshire and Iowa, the other states with gay marriage, have each voted Democratic in four of the past five presidential races.

Although some polls have found that modestly more Republicans favor gay marriages, red states remain resistant. Thirty states, the vast majority of them Republican-leaning, have barred gay marriage in their constitutions. Few, if any, seem poised to reconsider.

This pattern points toward a house divided on gay marriage—potentially for years. That prospect unsettles activists on both sides. Evan Wolfson, president of Freedom to Marry, a gay-rights group, says that while some might find state variation an acceptable equilibrium, “they are not people whose marriages are waxing or waning depending on where they are parking that day.”

On most comparable issues, such as abortion and interracial marriage, the courts or Congress ultimately established one national rule, even if some states continued to press against them, for instance by imposing stiffer restrictions on abortion. Today, the public-opinion trends suggest that an eventual national standard would more likely recognize than block same-sex unions. Many people would always oppose such an outcome. But a period of state experimentation that integrates gay marriage into daily experience for more Americans offers the best chance of minimizing the divisions that persist over abortion, long after Roe.

This article appeared in the Saturday, February 25, 2012 edition of National Journal.

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