The Democrats should be very worried about Chris Christie.
Based on his performance during the Sandy disaster, it's clear that Christie could not only win the support of most Republicans, but quite a few moderate Democrats as well. Unless the Democrats nominate a rock star like Hillary Clinton, and unless Christie has an as-of-yet unknown disqualifying scandal in his past, he has a strong shot for 2016.
To that point, however, there's a reason why Romney didn't pick Christie as his running mate. Perhaps there was a red flag in the vetting. Either way, the Democratic Party leadership ought to be courting Clinton because at this point, she might be the only firewall between Christie and the White House.
Adding... He was pretty funny on SNL, too.