If Mitt Romney wants to win the election and become president, he should come out and support gay marriage. Doing so will work not so much because it's consistent with conservative principle (which it is) and generally popular (that too) but because it will fracture Obama's base.
Let's start with why marriage is right from a conservative perspective. Conservatism is, as Russel Kirk wrote a "body of sentiments, rather than... a system of ideological dogmata." And, as such, it has to evolve with the times. In a very different society where two-parent marriage was essentially the only setting in which children could be raised, divorce was very difficult to obtain, premarital sex frowned upon by "respectable" people, and co-habitation without marriage virtually unknown amongst the well-educated; it's possible that having the state stand for one-man/one-woman-only marriage could make sense.
But that's not how modern society works. Gay and straight Americans alike enter into a lot of different types of partnership arrangements. Some of these are clearly undesirable. But others -- committed heterosexual couples who live together long-term without marriage, committed same-sex couples raising children together -- bring many of the same social benefits as marriage. Making these relationships stronger and granting them legal recognition is a good idea if one wants to create a society where families, houses of worship, and other voluntary institutions, not government, does most things.
Second gay marriage is a winning issue. In the wake of the President's announcement that he supports gay marriage, Americans' positions are changing -- quickly. For the first time, outright majorities of Americans in big, well-controlled national polls say that they support gay marriage. While simply looking at polls doesn't always tell you what will get votes -- easing of restrictions on gun ownership is generally unpopular but nonetheless a winning political issue for many candidates -- they're nonetheless a decent guide. And now, a majority of Americans want gay marriage.
This matters because current polls show Obama holding a rather narrow lead in the popular vote and a bigger one in the electoral college. Overall, this means that his positions and person are more popular than Romney's. The problem for Romney that much of President Obama's true base, a bit of 40 percent of the vote is simply not going to vote for Romney under any circumstances. Despite a lackluster economy, the President has delivered pretty well for union bosses, businesses that rely on government subsidies, government workers, current college students, and others who make up the Democratic base. For a variety of reasons -- including the historical nature of his presidency -- African-Americans (who, polls show, generally oppose gay marriage) can also be expected to cast ballots for Obama almost no matter what. The bottom line is simple: nothing Romney could do will dislodge most of the Democratic base and he's best off writing it off.
But gay voters are "getable" in significant numbers and could change the calculus. Beyond the party's acceptance of them as people -- an understandably big deal -- there is no reason why gay or lesbian Americans should necessarily belong to either party. Gay government workers, hard-core environmentalists, adherents of age religions, union bosses, and welfare recipients probably should and will vote for Democrats. Gay entrepreneurs, gun owners, pro-lifers, people of traditional faiths, and those just sick of being overtaxed will most often find their interests best met by the GOP. Right now, however, most people in the later group will still vote Democratic just because of the GOP's rejection of gay marriage. If one goes with low-ball estimates that somewhere around 2-3 percent of the population is gay (and it's probably twice that) getting even half of the gay vote would almost certainly put Romney over the top. And there's reason to think he could get more: Marketing data does generally indicate that gay couples are more affluent than the population as a whole and thus likely to benefit from the lower-tax policies that Romney would pursue.
While some voters would certainly be turned off by a Romney endorsement of gay marriage, many people concerned enough to vote against a rock-solid conservative like Romney over gay marriage alone might also vote against Romney for his Mormon faith or previous support for abortion. Sure, endorsing gay marriage has risks but, for Romney, it may be one of the few paths he has to the White House.