Chris Christie is a straight-talking Republican who prides himself on shunning politics as usual. Now he must explain his way out of a scandal that threatens to impede his path to the presidency.

For months, the governor of New Jersey has been hailed as the next great hope for his party, a blunt and charismatic politician who is unafraid to tangle with opponents, or even to reach out to Democrats.

Now that carefully groomed image is under threat – and Mr. Christie, in his own words, feels "humiliated" – thanks to a growing controversy over the most quotidian of problems: a massive, massive traffic jam.

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The snarl was initiated last year by his staff as an apparent act of political retribution targeting the mayor of the town next to the George Washington Bridge – precisely the kind of petty score-settling that Mr. Christie claims to shun. Seeking to contain the firestorm, Mr. Christie publicly apologized on Thursday and fired the aide responsible.

In a two-hour press conference on Thursday, he stated repeatedly that he had no knowledge of a plan to close two lanes leading to the bridge, the world's busiest span, which joins New Jersey to Manhattan.

"I am embarrassed and humiliated by the conduct of some of the people on my team," said Mr. Christie. "Ultimately I am responsible for what happens under my watch, the good and the bad."

The traffic bottleneck lasted for four days last September and paralyzed the town of Fort Lee, N.J., which is adjacent to the bridge. It delayed not just commuters but school buses and emergency responders. After his press conference, the Governor flew by helicopter to Fort Lee to apologize in person.

New Jersey is no stranger to sordid political scandals or high-flying politicians plummeting from grace. Despite Mr. Christie's public and humbling declaration of contrition, the political and legal blowback is unlikely to dissipate any time soon. Federal prosecutors in New Jersey have opened an investigation into whether the lane closings broke any laws and state legislators have already begun their own probe.

E-mails circulated on Wednesday showed that Bridget Anne Kelly, Mr. Christie's deputy chief of staff, instigated the lane closures as a form of punishment for the mayor of Fort Lee. The mayor, a Democrat, had declined to endorse Mr. Christie, who was then seeking re-election.

Mr. Christie said he was "blindsided" by the content of the e-mails, and called the traffic snarl-up a "rogue political action." He said he had fired Ms. Kelly for lying to him about whether she had any information on the lane closings. He also punished his two-time campaign manager, Bill Stepien.

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(In an e-mail sent days after the traffic jam, Mr. Stepien called Mark Sokolich, the mayor of Fort Lee, "an idiot." In response, Mr. Christie banished Mr. Stepien from broader roles in the Republican party).

For months, Mr. Christie had dismissed reports that the lane closings were politically motivated. He denied that any of his staff had played a role in the closings, which he described as part of a traffic study.

About a month ago, Mr. Christie said, he explicitly asked his staff if they knew anything more about the source of the snarl and received assurances that they did not. "I am a very sad person today," he said at the press conference. "A person close to me betrayed me, a person who I counted on and trusted."

Mr. Christie, who is considered a front-runner for the Republican nomination in the 2016 presidential race, said he only learned of the e-mails on Wednesday morning.

"Time for some traffic problems in Fort Lee," wrote Ms. Kelly in August to David Wildstein, a close ally of Mr. Christie's and a senior official at the Port Authority of New York and New Jersey, which controls the bridge. On Thursday, Mr. Wildstein refused to testify before state legislators, invoking his constitutional right against self-incrimination.

Mr. Christie said he was still unsure what exactly had led to the closures. "I don't know whether this is a traffic study that then morphed into a political vendetta, or a political vendetta that morphed into a traffic study," he remarked. (A senior Port Authority official appointed by New York's governor has testified that he was unaware of any legitimate traffic study connected to the lane closings).

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Mr. Christie also expressed confusion at why his staff would focus on the Fort Lee mayor, Mr. Sokolich. He claimed not to be able to recognize Mr. Sokolich and said he was unaware of any move to secure his endorsement.

During Mr. Christie's apology tour of Fort Lee, a town of 35,000 in the shadow of the bridge, he met briefly with Mr. Sokolich, the man whom the Governor's associates derisively called the "little Serbian" or "Serbia" in their communications (Mr. Sokolich is Croatian).

"Thank you for the apology, we are grateful for it," said Mr. Sokolich, who nevertheless called the visit premature. He added that it appeared that Mr. Christie's staff had used their power to engage in "venomous, petty" politics.