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Christie told a news conference he was stunned and heartbroken by revelations that his staff was behind the traffic jam designed to punish a local mayor who declined to endorse Christie's re-election bid. The office of the US attorney in New Jersey said it had launched an investigation.
The scandal and potential legal problems come as Christie has emerged as one of the most powerful figures in the Republican Party as head of its governors association and a possible contender for the White House in 2016.
"I am embarrassed and humiliated by the conduct of some of the people on my team," Christie said. "I am who I am, but I am not a bully."
Christie said he has dismissed his deputy chief of staff, Bridget Anne Kelly.
US Attorney Paul Fishman - whose job Christie held before he was elected governor - has opened a probe into the lane closures, his spokeswoman said.
"The Port Authority Office of Inspector General has referred the matter to us, and our office is reviewing it to determine whether a federal law was implicated," Rebekah Carmichael said in a statement.
The controversy erupted with the public release of incriminating emails showing that a top aide to Christie played a key role in closing some lanes to the bridge, in a ploy to punish the Democratic mayor of Fort Lee, New Jersey.
The George Washington Bridge, one of the busiest spans in the world, connects New York City to Fort Lee. The abrupt four-day lane closures in September caused hours-long traffic jams and held up the passage of school buses and ambulances.
A local newspaper reported that emergency responders were delayed in attending to four medical situations. One involved an unconscious 91-year-old woman who later died of cardiac arrest and another, a car accident, in which four people were injured.
Christie has enjoyed immense popularity at home since his election in 2009, particularly for his handling of recovery and rebuilding efforts after Superstorm Sandy devastated his state in late 2012. He was re-elected in a landslide in November.
He has also touted his ability to work with political opponents as a mark of his skill at overcoming partisan divisions and forging alliances to get things done.
But the blunt-talking governor is known as well for engaging in shouting matches, hurling insults and belittling challengers.
Now, the incident threatens to tarnish Christie's image and national standing as he weighs a 2016 bid for the White House. He told the news conference he was "nowhere near" beginning to consider a possible 2016 presidential bid.
"The problem for Christie is that this feeds into the pre-existing narrative that Christie is a bully, that Christie is a thug," said Doug Muzzio, a professor of public affairs at Baruch College in New York. "If I'm running in a primary in 2016, I'm going to be saying, 'Do you want President Vindictive?'"
Others took a more charitable view.
"My prediction? The whole thing will blow over," Republican consultant Mike Murphy wrote in the Daily News. "The question is how Christie's hands-on, full-volume personality will wear with voters over time."
At his news conference, Christie said he had been misled by his staff and knew nothing of the lane closings before they occurred and that he had been led to believe the closures were part of a traffic study.
He also said he was "blindsided" and heartbroken by the emails, and that he was doing some "soul searching."
"What did I do wrong to make these folks think it was okay to lie?" Christie said. "What I want the people of New Jersey to know is that this is the exception, not the rule."
In the most damning email, Christie aide Bridget Anne Kelly, wrote to a Port Authority executive in August, saying: "Time for some traffic problems in Fort Lee."
The executive, David Wildstein, replied: "Got it."