I would disagree with that in part. While one can postulate that the election freed up antigun forces, one could easily argue that one would not want to enrage progun forces to produce another legislative debacle in 2014.
That people are so sure of this outcome is known as hindsight bias. Of course, I know this now.
I think more important was the killing of the little children. They were innocent and to be horribly factual - high value, upper class kids in a seemingly safe environment. That set off some well know heuristics of horror - don't kill kids, don't kill high value members of society. The continuing slaughter of ghetto kids doesn't bring such outrage.
That was the trigger for the latent antigun proposals to spring into action. It overwhelmed some political considerations. Harry Reid and supposedly behind the scenes some Democrats are bringing this up.
If Sandy Hook didn't happen - it probably would have been business as usual - little done. I agree with Al that no one could have foreseen a catalyst of this specific parameters.
The crucial time will be on the Federal level, if senators or reps who were strong RKBA folks and then switched - get voted out of office in 2014.
The public and politicians will also be stampeded by some horror that reaches a high enough level.
To speculate - let's say Lanza was Islamic and was taken alive. He proclaimed his act was for his religious cause. Would there be an AWB push? Probably not - the dynamic would change and some folks might be asking for Japanese WWII interment camps or intense registration of Muslims, etc. Some would say that they knew all along that this kind of terrorism would happen.