Amusing; at least three Democrats (Biden, Cuomo, O'Malley) have now placed the gay marriage issue into their arsenal which they intend to use to jockey for 2016. Kirsten Gillibrand also used it as a career-booster, and has been mentioned as a possible 2016 contender as well, although less than the other two New Yorkers. I guess this must be low-hanging fruit for Dems who aren't in red states.
I don't see how the 2016 nominee wouldn't support gay marriage. Hillary or Schweitzer or other 2016 possibilities would presumably come out in support before they run (if they run). It should be easy for Hillary, her husband already supports it.