I expect Christie to switch parties at some point.
The democrats won’t let him run if he switches. They’ll despise him for his weight, and they’ll despise him for his past. He’ll get the Arlen Specter treatment, who was a huge public relations win for the Dems, but then they studiously ignored him after that. He’d served his purpose.
The democrats would shed blood before they’d let Christie have their presidential nod.