So he doesn't know about the lane closings when it first happens. Yet there is growing media noise about it and the legislature starts digging. He asks his aides, and they say "just politics, boss. We did nothing." He believes them. But ... four months later of increasing scrutiny, and he—a former prosecutor!—still doesn't get curious enough to start his own internal probe? He doesn't ask, "Was there REALLY a study, and if so, can you show it to me?" I find that hard to believe. Not knowing about the original closures? Plausible (whether likely or unlikely). Still not knowing what happened four months later, well, that stretches credulity to the breaking point.
Furthermore, why would his aides think it would be okay to screw some small-town mayor (and everyone else on that bridge) over a meaningless irrelevant endorsement? I mean, who expects endorsements from the rival party, and then gets so upset when they don't get it to go to such great lengths as this in retribution? And who gets excited at the idea of schoolchildren getting stuck on that bridge?
They thought it was fine because of the culture that Christie has created, one of intimidation and bullying. Remember that bullying incident where he screamed at the school teacher? That wasn't caught by a rival campaign tracker. That was caught on camera by a Christie staffer, and they put that stuff online. They're proud of that! So given that Christie once boasted that "for better or for worse, this staff will reflect my personal style of leadership and decision-making," it shouldn't be surprising that it reflected the worst of his personality. Or put another way, his staff didn't go rogue.
Now, his "I didn't know a thing" schtick, however implausible, at best paints him as a clueless dolt who can't handle his staff—completely counter to the persona he's built over the last several years as a hands-on in-the-trenches roll-up-your-sleeves-and-get-it-done governor. You can't be blissfully unaware of what your top staff is doing and then claim you are deeply involved in the governing business.
But worse for him, the "bully" narrative is now set in stone. It was his greatest source of strength but now it's been neutered. I doubt his staff will be posting any other YouTubes of him being a dick to ordinary people. Good luck with that.
Finally, notice how lonely Christie looks today? No one is defending him, not even Republicans. There are too many interests in his party vested in his failure ahead of 2016. The tea party crowd is suddenly pretending to care about Christie being a bully, as if they don't love people who are dicks to liberals. The establishment would love to have a viable nominee, but those supporting the likes of Jeb Bush and Marco Rubio are twisting the knife. The Christianist Right is similarly gleeful.
So he's been left alone, flailing, leaving people to debate the title of this post.