I've heard rumors for a while that Christie had a scandal similar to this in the making, and I assumed that Bridgegate was the scandal in question. This doesn't surprise me if true, and I'm sure more will come of it.
There was (and likely still is) a number of potential skeletons in Christie's closet that kept Romney from tapping him as veep. Since Bridgegate happened almost a year after the election, it's just another strike against him.
There's no telling what else is going to come up if and when Christie runs for president. That's why these claims of electability are extremely exaggerated. Early polls may be of little value, but if anything, they serve to debunk those claims.
