Sometimes in politics, you have to listen for what’s not being said to understand how things really stand. In the 2012 presidential campaign, the telling — and comforting — silence involves same-sex marriage and gay rights.

Think about it: In 1992, Pat Buchanan, speaking at the Republican convention in Houston, warned that Bill Clinton wanted to impose a “homosexual rights” agenda on America.

In 2004, Republicans engineered ballot initiatives against same-sex marriage in 11 states, hoping to bolster George W. Bush’s reelection chances by spurring conservatives to go to the polls.

It may not have worked — former Bush adviser Matthew Dowd has written that the initiatives “had no discernable effect on turnout among conservatives” — but those ballot initiatives didn’t turn up by accident.

Flash-forward to 2012. President Obama pushed to lift the ban on gays serving openly in the military, undoing the “don’t ask/don’t tell” policy put in place by the last Democratic president. He instructed the Justice Department to stop defending the constitutionality of the Defense of Marriage Act (DOMA), also signed into law by President Clinton. Obama completed his slow evolution on same-sex marriage and came out in support.

The platform approved at the Democratic convention in Charlotte included a plank supporting same-sex marriage. Last week, Obama urged voters to back initiatives in Maryland, Maine and Washington state to allow gay couples to marry; he had previously urged Minnesotans to vote against a marriage prohibition.

If this is exacting a political price, it’s hard to discern. Republicans and their nominee, Mitt Romney, have not raised the subject — not at their convention, not on the campaign trail, not during the debates.

“It just shows how different the politics are, and how profoundly the center of gravity on the freedom to marry has shifted,” said Evan Wolfson, president of Freedom to Marry. Gay rights and the right to marry, he noted, “used to be something Republicans campaigned on, and Democrats wanted to be on the right side but didn’t want to talk about it. Now it’s the exact opposite because a majority of the country favors it and a majority of independents favor it.”

The difference is striking. I remember questioning a parade of Democratic presidential contenders about same-sex marriage during the 2004 campaign. They would stammer and talk about hospital visits, maybe civil unions. Their aides would glare at me for broaching this unwelcome topic.

The Republican Party hasn’t transformed itself — far from it. The party platform calls for a constitutional amendment to define marriage as the union of one man and one woman. Romney has signed a pledge from the National Organization for Marriage to back the amendment and support DOMA.

Still, said Chad Griffin, president of the Human Rights Campaign, “this is the first time we have seen a major national election in which one party has not overtly attacked LGBT people and opposed their equal rights in order to gain votes and motivate a base.”

The most interesting test involves the marriage initiatives on the ballot in four states (Maine, Maryland and Washington, where voters are being asked to affirmatively support same-sex marriage, and Minnesota, where opponents of marriage equality have an initiative to prohibit it).

In 32 out of 32 previous ballot initiatives — including an attempt in Maine just three years ago — voters have rejected same-sex marriage. Now, that string of intolerance may be broken; polls are tight in all four states.

But the message of those opposing same-sex marriage has shifted — to emphasize tolerance but draw the line at marriage. One spot against the Washington state measure opens with a rainbow flag, and assures voters, “Gays and lesbians already have the same legal rights as married couples. . . . You can oppose same-sex marriage and not be anti-gay.”

Polling explains this soft sell. A new report from the centrist Democratic group Third Way shows that most of the increase in support for marriage equality comes not from the changing demographics of younger voters, who are more open-minded, but from older voters reconsidering. “Americans in every demographic, political and religious group across the country are changing their minds on this issue,” the report found.

In 2004, 16 percent of Republicans backed same-sex marriage; by 2011, 26 percent did. In 2004, 33 percent of self-described moderates supported marriage equality, by 2011, 54 percent were in favor. And although the Catholic Church is a major financial backer of groups opposing same-sex marriage, support among Catholics has grown from 35 percent to 52 percent.

From ultimate wedge issue to relative nonissue — a stunning transformation.