That sound you don’t hear is social change happening.

Even as the Republican candidates fight to see who can get furthest to the right, acceptance of gay people and gay marriage in the United States is moving briskly along. Gallup finds support for same-sex marriage now at 53 percent, up from 40 percent in 2008.

In February alone, a federal appeals court ruled California’s gay-marriage ban unconstitutional; Washington state legalized gay marriage; New Jersey’s Legislature passed a marriage law (vetoed, though with a caveat, by Gov. Christie); and a marriage-equality law passed the Maryland legislature and became law on Thursday.

As voters’ attitudes change, politicians are changing too. In 2008, both Barack Obama and Hillary Rodham Clinton opposed equal marriage rights. But now two governors with presidential ambitions have very visibly invested political capital in supporting gay marriage.

In New York, Gov. Andrew Cuomo took personal command of the campaign for marriage rights. He made speeches, twisted arms, calmed Catholic opposition, plotted with Republican donors, and got the credit when it passed. He was immediately hailed as a front-runner for the 2016 Democratic presidential nomination.

Not to be outdone, Maryland Gov. Martin O’Malley announced he would make marriage equality a top priority for the 2012 legislative session. After appealing to Maryland’s heritage of religious freedom and “respect for the freedom of individual conscience,” he signed the bill into law Thursday.

Republicans haven’t given up their opposition, but their resolve is weakening. A few GOP legislators helped put the issue over the top in New York, Washington, and Maryland. Former Republican national chairman Ken Mehlman and a group of libertarian-leaning GOP donors played a key role in Cuomo’s efforts in New York.

The formerly vocal opposition to gay marriage has quieted. Congressional Republicans haven’t revived the Federal Marriage Amendment. Conservative media stalwarts like Rush Limbaugh and Bill Buckley’s National Review have barely mentioned the issue. (When you search for gay marriage at National Review Online, you get lots of ads for things like “Gay Destination Weddings.”) The ambitious Christie vetoed his state’s bill while also calling for a referendum on gay marriage rather than flatly rejecting the idea. He also has nominated an openly gay judge to the state Supreme Court.

Even Rick Santorum, who has been stridently antigay throughout his career, muted his remarks when he led a rally to repeal the Washington state law. “There are legitimate reasons that people have to want… to change the law,” he said. “And there are legitimate reasons that people have to want to keep the law in place… There are ebbs and flows in every battle.”

Republican leaders know that opposition to same-sex marriage is strong in their base right now but that young voters support marriage equality overwhelmingly. They don’t want to lose a whole generation.

Just two decades ago most Americans said they didn’t know anyone who was gay. Now only 22 percent say that — a remarkable level of change. Acceptance and visibility rise in tandem.

The shift in mores has been even more pronounced in commerce. One telling episode is J.C. Penney Co.‘s hiring of openly gay talk-show host Ellen DeGeneres as a spokeswoman. Penney’s demographic is Southern and Midwestern middle-class moms. A small band of social conservatives went ballistic. The “One Million Moms” project of the American Family Association called for a boycott, but no mainstream conservatives seemed to notice.

As Bill O’Reilly noted, the One Million Moms couldn’t produce a single one to go on his popular Fox News Channel show. He did find a defender to appear in their stead, and he and conservative media critic Bernard Goldberg proceeded to denounce McCarthyism, blacklisting, “witch-hunts,” and “a strain of bigotry running through conservative America.”

Other corporations have been even more outspoken. New York Times columnist Frank Bruni writes that several large corporations, including Starbucks, Microsoft, and Amazon, backed gay marriage in Washington state. Bruni points out: “More so than politicians, corporations play the long game, trying to engender loyalty for decades to come, and they’re famously fixated on consumers in their 20s and 30s. They see support for same-sex marriage as a winner, something that will help with employee recruitment as well.”

If the federal court decision holds up in California and gay marriage is restored there, then almost a quarter of Americans will live in states with marriage equality.

That sound you don’t hear — the absence of outrage over marriage rights, and gay spokespeople for middle-American companies — is the sound of social change.