I suspect that you're right. He can't blow off his core constituency without repercussions, but he did manage to deflect their request that he do something by telling them that, if they wanted to do it, they would need to amend the constitution. It was a good answer, because it throws the ball out of his court, and a 'Defense Of Marriage' amendment is very unlikely to pass -- or even come to a vote, for that matter. The state amendments of that type have, for the most part, been struck down in court.