Governor Chris Christie’s darkest moment, at least in the eyes of some members of the Republican establishment, came on a chilly Sunday night in early November of last year, just days before the presidential election. What Christie and his team did that evening, in a series of terse e-mails and calls with the pleading Romney camp, remains murky. On Capitol Hill, insiders still treat the episode like the Zapruder film, analyzing it and trying to discern, from limited context, what exactly happened. But what didn’t happen is indisputable: Christie didn’t attend Mitt Romney’s rally at Shady Brook Farm in Lower...