"I told Governor Romney at that time that if the storm landed as predicted that it was going to be catastrophic to New Jersey and unprecedented," Christie said. "I said to him, 'Listen, Mitt, if this storm hits the way I think it's going to, I'm off the campaign trail from here to Election Day.' And he said to me, 'Chris, of course. Do your job, don't worry about me. I'll take care of things.' So all this other noise, I think, is coming from know-nothing, disgruntled Romney staffers who, you know, don't like the fact that I said nice things about the President of the United States. Well, that's too bad for them."
Maybe Christie is deliberately trying to sabotage Romney so he can have his shot in 2016.
Maybe he's just trying to shore up his favorables in NJ for his own re-election as Governor.
Maybe, just maybe, he really does care more about the well-being of his own state and the people of New Jersey (y'know, doing his job) then his political future.
Quite possibly it's a mix of all 3 of the above.
Ultimately, though, it doesn't really matter. It's just fun to watch :)