It does not even have to be that big in order for it to be devastating - he needed a good performance to keep his momentum going and he didn't get it.
He doesn't need to win New Hampshire, he just needs to do better than the other establishment candidates. If they perform poorly then they will drop out and that support will go to Rubio. This is all he needs. If this gaffe is bigger than I think it is and propels Christie to competitive levels with Rubio then that could be it, but I just don't see that happening.
Yeah finally someone else on this forum says it. I really don't think this is that bad and the idea that it is candidacy ending or even CAREER ENDING is total tripe. I will concede that one worrisome element for Rubio is that it helps Christie at his expense which like you say could hurt his chances if Christie pulled a miracle out in NH. But seriously guys, this was just another gaffe. It was a pretty bad one, put this is not gonna be a turning point in the campaign.