This is an issue on which the fundamentals of public opinion change glacially. Support for same-sex marriage is rising, but only by about a percentage point or so a year. Essentially, a third of the public supports gay marriage, another third or so supports civil unions instead, and the remaining third opposes any kind of legal status for same-sex couples. Although public-opinion fundamentals didn't change in 2009; the politics of gay marriage did. Here are the ways the year marked a shift to what a storyteller might call the 'long middle.' The preemptive strikes on both sides have failed. Early on, conservatives feared that courts would impose same-sex marriage nationally by fiat. They responded with an attempt to ban gay marriage nationally by constitutional amendment. But the federal courts kept their distance, and the amendment was rebuffed. As the year ends, it is clear that neither side can knock the other off the field. Gay marriage is firmly established in five states (with the District of Columbia's likely to follow suit), but it is banned, often by constitutional amendment, in most of the others. Unless the Supreme Court shocks the country and itself by declaring gay marriage a constitutional right, the issue will take years, perhaps decades, to resolve. All-or-nothing activists will be disappointed, but the country will get the time it needs to make up its mind. Legislators are taking over from judges. For years, the only way same-sex marriage seemed possible was by court order. But with state venues for pro-gay-marriage lawsuits having just about dried up, the fight has moved from the lower courts to the political branches, much as the civil rights struggle did in the 1960s. Now, as then, legislative victories afford the movement more momentum and popular legitimacy than judicial ones ever could. Opponents were fond of arguing that the gay-marriage movement was not just wrongheaded but antidemocratic. But in 2009, gay marriage was passed by the legislatures and signed into law in Maine and New Hampshire, and it was enacted by a veto-overriding majority in Vermont. Nothing undemocratic about that. Same-sex marriage has been mainstreamed. In its first decade or so on the national stage, gay marriage was a fringe idea, the property of the political far left. No longer. Gay marriage may still be losing at the ballot box, but in Maine in 2009, as in California in 2008, the margins have grown tight. With its establishment last spring in Iowa, same-sex marriage has penetrated the heartland, by court order but with little backlash. Many Democrats have come to see support for gay unions as a political plus. Increasingly, it is the opponents who are playing cultural defense, insisting that they are the ones who are being marginalized and stigmatized. There's a backlash against the backlash. The most important trend of 2009 began Nov. 4, 2008, when California voters passed Proposition 8, revoking gay marriage in their state. Until then, the preponderance of passion lay with opponents. After Proposition 8, however, many heterosexuals embraced gay marriage, taking ownership of an issue that they have come to view as the next great civil rights battle. For same-sex marriage advocates, the emergence of a dedicated core of straight supporters is a sea change. There is now comparable energy and commitment on both sides. It was just such passion, indeed, that led two of the country's most distinguished lawyers -- Theodore Olson, a Republican, and David Boies, a Democrat -- to join hands across party lines in 2009 and file a lawsuit asking the federal courts to overturn California's Proposition 8. The case is a long shot legally, but the fact that it has attracted such solidly mainstream legal talent is one more sign that the same-sex marriage issue has come of age. Jonathan Rauch, a guest scholar at the Brookings Institution, is the author of 'Gay Marriage: Why It Is Good for Gays, Good for Straights, and Good for America.' 