Rick Santorum is at it again, fighting gay marriage with arguments that don’t hold up to scrutiny. And these days Republicans are keeping their distance.

Santorum writes:

Social science provides overwhelming evidence of the benefits of marriage to children and society. In what other area of public policy would government be neutral when the benefits are so overwhelming? We know work and marriage are antidotes to poverty… Research tells us that low-income children without a father at home are five times more likely to remain poor.

But his solution to this problem is a ban on gay marriage. What’s the connection? It isn’t gay couples who are raising single-parent children, who are more likely to encounter problems with school and the law. Much of the argument for gay-marriage bans is this sort of bait-and-switch: point to a real problem, then come up with an irrelevant solution that scapegoats a small group.

Fortunately, Republicans are mostly ignoring Santorum and his allies these days. They see the long-term damage that the anti-gay crusade is doing them. Back in 2004 they thought that social issues, especially gay marriage bans, would help them win the presidential election. It wasn’t really true even then: it turns out that George W. Bush’s share of the vote rose just slightly less in the marriage-ban states than in the other states: up 2.6 percent in the states with marriage bans on the ballot, up 2.9 percent in the other states.

This year, even though President Obama and the Democratic platform have endorsed marriage equality, Mitt Romney and the Republicans are staying away from the issue. With good reason. The Washington Post reported earlier this month:

In February, a poll by the [Des Moines Register] newspaper found that 56 percent of Iowans were opposed to legislative efforts to pass a constitutional amendment to ban same-sex marriage. That is consistent with other swing states: Voters back gay marriage by 21 points in Florida, 15 points in Ohio and nine in Virginia, new Washington Post polls found.

Read that again: “Voters back gay marriage by 21 points in Florida, 15 points in Ohio and nine in Virginia.”

A September Post poll in the crucial state of Ohio found that by 61 to 30 percent, registered voters said they trusted Obama “to do a better job dealing with social issues such as abortion and gay marriage.”

A late October poll found that in swing-state Virginia

Obama also enjoys a wide lead among likely voters (56 percent to 35 percent) on the question of social issues, such as abortion and same-sex marriage.

Nationally, a Post poll analysis found that 63 percent of the tiny number of genuine swing voters support gay marriage.

I argue in my new ebook, The Libertarian Vote: Swing Voters, Tea Parties, and the Fiscally Conservative, Socially Liberal Center that 15 to 20 percent of the voters hold broadly libertarian views, conservative on economic issues and liberal on social issues. They usually vote Republican, if the Republicans emphasize fiscal issues and soft-pedal social conservatism. Republicans are starting to notice that. And they know that, even as support for marriage equality is just flirting with 50 percent, two-thirds of young voters support it. Campaigning against gay marriage is a good way to make the Democratic advantage among young people permanent.

That sound you don’t hear, the missing Republican ads denouncing Obama for his support of gay marriage? That’s the sound of social change. It looks like Rick Santorum is being left behind.