Champagne corks were popping last week among supporters of same-sex marriage. No wonder: In the span of five days, the number of states where gays and lesbians could tie the knot doubled, from two to four. The Supreme Court of Iowa, a state not usually in the progressive vanguard, declared that gays had a right to marry. A few days later, Vermont's lawmakers, profiles in courage who overrode a governor's veto, voted to let same-sex couples marry; that marks the first time a legislature (rather than a court) has led the charge. Exuberant advocates saw these landmark events as marking a turning point in the same-sex-marriage campaign.

It's a nice thought, but far too rosy. Nationwide, same-sex marriage may well be a generation away.

In the short run, the prospects for same-sex marriage do look good. The bitter disappointment following November's vote onProposition 8, when 52 percent of the California electorate inscribed "marriage is for straights" into the state Constitution, has receded. Rejuvenated same-sex-marriage advocates predict that New York, New Jersey, Maine and New Hampshire will soon join the same-sex-marriage bandwagon, and the California battle will be refought in a few years. In only half a decade - mach speed for such a divisive moral issue - national support for same-sex marriage has climbed 10 percentage points, to 44 percent. With younger voters more inclined to favor gay rights, this support should keep increasing.

While that's all true, it's just a sliver of the truth.

Aside from Iowa, the present (Massachusetts, Connecticut, Iowa and Vermont) and prospective pro-gay marriage states are the usual suspects: the Northeast, which right-wingers would love to saw off the continent and send out to sea, and the West Coast. Elsewhere, it's an entirely different story.

In 2004, after the Massachusetts Supreme Court became the nation's first tribunal to recognize same-sex marriage, the opponents mobilized. Well-heeled and well-organized, they convinced voters in 26 states to rewrite their constitutions, defining marriage as a heterosexuals-only affair. Anticipating a pro-same-sex marriage decree, three states had already passed such amendments. And a half dozen states don't even protect gays against discrimination.

Iowa is the proverbial exception that proves the rule. Same-sex marriage advocates targeted the Hawkeye State because its court leans left and because it takes at least two years to amend the state constitution. The first same-sex weddings will be held there in a few weeks, and maybe the sight of happily married gay and lesbian couples will warm Iowans' hearts, but outside the Northeast and California, prospects are much bleaker.

Over time, this picture will change - that's what the shift in attitudes means - but the change will come slowly. In an earlier era, backers of same-sex marriage would have gone to the Supreme Court, just as abortion-rights advocates did, but for now the Supreme Court is to be avoided at all costs.

Political mobilization - persuading the voters to rewrite their state constitutions - is the most promising way to make America a same-sex-marriage-friendly nation. Such retail politics will be slow going. Yet as Matthew Coles, director of the ACLU's Gay and Lesbian Rights Project, points out, it's how to win hearts and minds - "not by talking about abstract issues but about the ordinary lives of gay people and how being gay makes life harder." Those will be tough conversations, but the events in Iowa and Vermont make a great conversation-starter.

David L. Kirp, James D. Marver professor of public policy at UC-Berkeley, is the author of the upcoming "Improbable Scholars: The Rebirth of a Great American School System and a Strategy for America's Schools." This article was originally posted on SF Gate.