New York could legalize gay marriage as early as today or tomorrow, if Senate Republicans agree to hold a vote on it, which seems increasingly likely. So how does this affect the national scene?

I’m going to suggest that it seems fairly likely that we’re in for a round of gay-bashing — or at least, a strong focus on issue involving gays and lesbians — before the GOP presidential primaries are through.

Here’s the situation: the nature of primary elections, from president on down to local races, is that candidates with very similar views compete to differentiate themselves. Are there serious differences in issue positions on public policy separating Mitt Romney, Tim Pawlenty, Rick Perry, and even Michele Bachmann and Rick Santorum on the one hand or Jon Huntsman on the other? For the most part, no.

This leaves candidates other than the frontrunner with a problem, however; if everyone agrees on the issues, why not just vote for the leader? The solution is generally to invent differences. Sometimes, that involves true issue innovation. That’s hard work, however, and sometimes risky. That’s why candidates fall back on a number of traditional tactics. They can split hairs: my nearly identical proposal on taxes is far more orthodox than the other guy’s. They can argue authenticity: our positions on abortion may be identical now, but I’ve held my position far longer than she has. Or they can argue emphasis: I’m the only one on this stage willing to talk about this issue, which shows I’ll actually carry out my plans if elected.

For social conservatives, sexual orientation is a natural topic for all three of these tactics, but especially the third. Frontrunner Mitt Romney surely doesn’t want to talk about any of it: marriage, military service, and certainly not basic questions of morality. Not only are social issues a relative weakness for him within the GOP, but as a potential candidate in the general election he doesn’t want to be identified as someone focused on those issues; he will want to run a campaign based on complaints about Barack Obama’s handling of the economy. And yet while the polls have shifted in the electorate as a whole, there’s good reason to believe that for social conservatives, sexual orientation is just as important an issue as ever.

To put it another way: whereas ten or twenty years ago Democrats had trouble with gay rights because the electorate as a whole opposed the relatively narrow majority within the Democratic Party, now it’s probably the other way around.

Mitt Romney’s real problems in the Republican primaries are probably centered on abortion more than anything else. But I’d expect at least one of the other prominent candidates to press him hard on issues involving sexual orientation sometime in the next several months. Bachmann, Cain, Santorum, perhaps even Perry or Pawlenty — the incentives are strong for one of them to appeal to anti-gay bigotry. And the legalization of gay marriage in New York just may give them the perfect opening to do that.