Rick Santorum’s round of verbal fisticuffs Thursday with college students in New Hampshire again proves that he won’t shift his socially conservative views to match the state he’s running in. That mark of virtue will cost him votes Tuesday.

It’s no surprise that Santorum has faced a barrage of criticism in the Granite State for his support for traditional marriage. New Hampshire is one of three states that have legalized same-sex marriage by legislative vote rather than judicial intervention. The Republican primary electorate’s libertarian instincts is significantly different from that of Iowa and South Carolina, where evangelical Christians carry more clout.

Even so, Santorum didn’t hold any punches last week when he engaged in a back-and-forth with students over same-sex marriage and polygamy. His adversaries in the crowd contended that Americans’ right to pursue happiness means that government must recognize same-sex unions. Santorum took that line of reasoning a step further: If happiness is the basis of state-recognized marriage, what’s the practical difference between homosexual marriage and polygamy?

It’s a legitimate point that gets to a core issue of the marriage debate: What constitutes marriage from a societal standpoint? Supporters of traditional marriage often point to factors beyond love, such as procreation. Love is obviously a critical part of any good marriage, but from a societal standpoint, it’s secondary. One of the primary reasons for the state to recognize marriages in the first place is that heterosexual marriage produces children. Even in situations where a couple can’t procreate — or choose to not do so — the biological mechanics are there for the perpetuation of the human race.

Because supporters of same-sex marriage can’t make that same claim, they resort to basing the core fundamental of marriage on love. Fine. But what if a polygamist loves his partners? What if he is in a committed, long-term relationship with them? If homosexuals’ right to pursue happiness is infringed by government’s refusal to recognize their unions, then polygamists’ right to happiness also is abridged.

The trouble for liberals is that the idea of polygamy gives them pause. They feel comfortable with same-sex marriage, but polygamy is a bridge too far. That could very well change in a few decades. Years ago, the idea of same-sex marriage was foreign even to many on the left. For now, though, they don’t like the concept, or at least don’t like the political unpopularity of it.

The frustration over Santorum’s point — and the frustration was obvious, as the college student struggled to answer — doesn’t change its legitimacy: If legal recognition for same-sex relationships is required, the same standard must apply to polygamy in order to maintain a coherent line of reasoning.

That said, it’s a nuanced point that most people won’t take the time to understand. And leftists’ narrative — denouncing Santorum for comparing homosexuals to polygamists — obviously will play better with the media, and with many voters in New Hampshire.

Despite his socially conservative views, a CBS News Poll puts Santorum in the top-three tier of candidates, a few percentage points behind Mitt Romney and Newt Gingrich. Santorum’s current standing of 14 percent is a huge jump since mid-September, when he polled at only 1 percent.

The RealClearPolitics polling average puts Santorum in second place, though barely. Romney will win New Hampshire, but second and third place showings Tuesday will go a long way in deciding whether Santorum will be the Mike Huckabee of 2012 — a socially conservative Republican who surprises in Iowa, then fades in New Hampshire and South Carolina — or a different force altogether.

Regardless of the results, it’s refreshing to see a national Republican candidate stick to his guns on positions he cares deeply about, even if they aren’t as popular with primary voters in New England.