'They' are destroying Christie's chances the same way 'they' destroyed Nixon's chances of staying office after Watergate. If a political office uses it's influence to punish, intimidate, or as some sort of payback I can see an investigation. However if 'they' go to the extreme Kenneth Starr did in the White Water business then I'd agree it has gone from investigation to trying to end Christie's political career.
Now if I had to opine on the push behind it, rather than blame the democrats, who Christie loved bashing going into office the first go-round, that old CON song and dance (Personal responsibility) is a better angle.... Christie prides himself on being no better friend and no worse enemy, I can't help but think his staff thinks the same way and gave a democratic mayor a taste of the latter.
Christie is GTG IF no one can prove he had anything to do with the lane closures, or if he ever knew it was going on. He walks away fat and happy IF no one can prove he has lied about his lack of role or knowledge.
Nixon didn't lose his office because he ordered or even knew ahead of time about the break-in, he lost his job because of his actions AFTER the bungled break-in.