BIZARRE AND outrageous as it is, the notion that political appointees at the Port Authority of New York and New Jersey engineered a huge traffic jam to get even with a local mayor would not normally dominate national news. What sets apart the multiday backup in September in Fort Lee, N.J., is that those who allegedly plotted it are close to New Jersey Gov. Chris Christie, an early front-runner for the 2016 Republican presidential nomination and, according to a new Quinnipiac University poll, the best-liked possible candidate of any party.

But the scandal that threatens Mr. Christie’s prospects — and forced him to explain himself in a lengthy news conference Thursday — is of interest for another reason, too: what the governor represents in U.S. politics. For all of his operatic and imperious ways, Mr. Christie was the leading centrist within a GOP that is listing dangerously right. All Americans have an interest in the survival of a moderate wing.

We certainly didn’t agree with everything Mr. Christie did during his first term. He vetoed the long-planned construction of a needed rail tunnel under the Hudson River; he waffled on offering in-state tuition at New Jersey’s public universities to the children of illegal immigrants. Still, his record reflects an admirable streak of independence. His first term was spent trying to stabilize a spendthrift state’s finances and shake up its dysfunctional institutions — public education, especially. In pursuit of these goals, he worked with Democrats in the state legislature. He appropriately reached out to President Obama after Hurricane Sandy, even at the expense of being vilified by his own party. He eventually signed a tuition bill for illegal immigrants that was a more rational approach toward the “dreamers” than many others in the GOP back.

Even the governor’s bully-boy reputation might be explained, up to a point. Politics ain’t beanbag. But there is a difference between using the levers of power to achieve policy goals and abusing them for petty payback, as Mr. Christie’s lieutenants apparently did. Limiting access to the George Washington Bridge, on the pretense of doing a traffic study, made children late for school and delayed first-responders. It harmed the people Mr. Christie is sworn to serve.

He made a start toward recompense Thursday by apologizing, firing a deputy chief of staff who, he says, concealed her knowledge of the scheme from him, ousting his top political aide and promising to cooperate with state and federal investigations. In denying any knowledge of the alleged plot, Mr. Christie staked his future on a claim of ignorance that many find implausible and that amounts to a plea that he failed as a supervisor. No evidence contradicts Mr. Christie’s version; if it’s a lie, it’s an unfathomably reckless one.

Still, the investigations need to proceed. If his subordinates didn’t act with Mr. Christie’s knowledge or approval, what did motivate them? If the questions can be answered satisfactorily, Mr. Christie may survive to carry the flag for the center-right. If not, he’ll have to make way for someone else.