A panel of Idaho Republicans want the state to rewrite its marriage laws to hold that it is "a bond between a 'naturally born' man and woman". (Via). Part of me hopes that this does pass, just because I think that it may actually be more vulnerable to challenge than typical laws "merely" prohibiting gay marriage. Because the law at least potentially prevents transgender individuals from marrying anybody -- man or woman -- it doesn't even have the (facially ridiculous) defense that it doesn't exclude anyone from marriage (just their preferred partner). If that's the case, it is tough to see it standing against constitutional challenge. And that, in turn, would be one hell of a precedent.
Then again, maybe I'm being too indulgent in formalist fantasies. Transgender rights are still pretty controversial, and I suspect a reviewing court, particularly in Idaho, will search long and hard for a "neutral" reason for upholding this law too. Best to not push my luck.