[P]erhaps, as Greg Sargent argues (hopes?), the next G.O.P. primary will be consumed by a debate over a federal marriage amendment and other anti-S.S.M. unicorns. But most likely not: The typical religious conservative of my acquaintance considers the battle lost, Fox News and other tub-thumping outlets have never much cared for the issue anyway, and ambitious Republican politicians will be happy to stop talking about it (as they mostly have already).
On the one hand, this is probably correct: it is unlikely that the political coverage afforded to the opposition to gay marriage will prove as durable as, say, that provided to the opposition to abortion. The debate going forward, to the extent there is one, will concern the extent of the protections given to dissenters, as Ross acknowledges.
But it is fanciful to imagine that Republican politicians will be allowed to slink away quietly. If the media debate moderators can find the space to ask Republican candidates if they "believe in evolution", a question of provably zero political relevance, I can promise that they will make a point of asking them if they support gay marriage.
And the answer matters. It is one thing to read Ross admitting that we are almost certainly going to lose. It's quite another to listen to a politician seeking my vote avow that, notwithstanding that he's "personally opposed"*, he supports gay marriage politically. It is possible that a candidate's positions on other issues might be sufficiently strong -- e.g., supporting an immmigration moratorium** -- that I would ignore his surrender on gay marriage, as a practical matter it isn't very likely.
So Republican candidates had better starting thinking now how they are going to deal with this question.
* Readers of a certain age will recognize this formulation, popular among "moderates" of both parties in the 80s, as a attempt to finesse the abortion issue. It actually worked for Carter in '76, but by 1980 pro-life voters had become too sophisticated to fall for it. That didn't stop politicians from trying it, however.
** In point of fact, I have despaired of the possibility that the Republican nominating system will yield a candidate credibly strong enough on immigration to tempt my general election vote, irrespective of gay marriage or any other issue on the horizon.