Biden opened up a can of worms with his fat mouth this time. God Bless 'im. He dared to make a statement that shines a light of hypocrisy on one of the Left's pet causes. 
The hard-Left believes their hard-Left President ought to fully endorse homosexual marriage, and he has not. They rightfully perceive that either he supports homosexual marriage and is politically fearful to admit it, or he does not support homosexual marriage, and is politically fearful to admit it. Based on his actions, I would say that those who believe him to support it in fearful silence are correct.
Biden may as well have gone to the press and said, "So, what about gay marriage anyway, Barack?"