Why is support for same-sex marriage declining?

The latest Gallup results on same-sex marriage are particularly interesting.  After years and years of growing popularity, it has slipped back somewhat (though, with still clear majority support) because Republicans have turned against it in surprisingly large numbers:

Republicans have gone from 55% to 46% in just two years.  What would cause this shift after such a long period of generally steady increase.  Hard not to conclude that it’s elite Republican opinion saying, “hey, those gays really aren’t so great after all!” of which there’s a lot going around.  I also cannot help but wonder if part of this is not somewhat of a backlash to transgender issues among Republicans even though same-sex marriage is really quite distinct, policy-wise.  Regardless, an interesting development.  And, to be fair, the Democratic increase has dropped off a bit, too (though not nearly as dramatically).  So, yeah, probably some culture war backlash here.