They mobilized the youth vote. Axelrod had done it in MA when he ran Patrick. Obama lost the over 60 vote 47/51.
The Catholic vote also decided the issue. Obama got 54%. They are the swing vote in American politics.
Before my Catholic friends get upset let me add that, among Catholics who attend Mass one or more times a week, Obama lost in a landslide. He won because of cultural/ethnic Catholics who may not have been to Mass in decades. Pew has the religious vote here
thank you for the clarification