New Jersey Gov. Chris Christie speaks during a news conference Thursday, Jan. 9, 2014, at the Statehouse in Trenton, N.J. A day after revelations that Christie's administration may have closed highway lanes to exact political retribution, the prospective Republican presidential candidate is faced with what may be the biggest test in his political career. New Jersey Gov. Chris Christie enters a news conference Thursday, Jan. 9, 2014, at the Statehouse in Trenton, N.J. Christie has fired a top aide who engineered political payback against a town mayor, saying she lied. Deputy Chief of Staff Bridget Anne Kelly is the latest casualty in a widening scandal that threatens to upend Christie's second term and likely run for president in 2016. Documents show she arranged traffic jams to punish the mayor, who didn't endorse Christie for re-election. New Jersey Gov. Chris Christie walks to the podium before a news conference Thursday, Jan. 9, 2014, at the Statehouse in Trenton, N.J. Christie has fired a top aide who engineered political payback against a town mayor, saying she lied. New Jersey Gov. Chris Christie speaks during a news conference Thursday, Jan. 9, 2014, at the Statehouse in Trenton, N.J. Christie has fired a top aide who engineered political payback against a town mayor, saying she lied. A car uses an onramp to the George Washington Bridge toll plaza in Fort Lee, N.J., Thursday, Jan. 9, 2014. The onramp was closed for three days in September 2013 snarling traffic at one of the world's busiest bridges, which links New Jersey and New York City. New Jersey Gov. Chris Christie faces political fallout over the traffic jam that caused hours-long backups for commuters and others as children started the school year. (AP Photo/Richard Drew) TRENTON, N.J. (AP) - Moving quickly to quell a widening political scandal, Gov. Chris Christie fired one of his top aides Thursday and apologized repeatedly for the "abject stupidity" of his staff, insisting he had no idea anyone around him had engineered traffic jams as retribution against a Democratic mayor. "I am embarrassed and humiliated by the conduct of some of the people on my team," the Republican governor said at a news conference in which he patiently took questions from reporters - and answered in his typically blunt fashion - for nearly two hours. Christie, who had previously assured the public that his staff had no involvement in the lane closings last September that caused major backups at the George Washington Bridge, said he fired Deputy Chief of Staff Bridget Anne Kelly "because she lied to me" when he demanded weeks ago that anyone who knew anything about the episode come forward. Kelly was the latest casualty in a scandal that threatens to upend Christie's second term and his expected run for president in 2016. Two other top Christie appointees have resigned in the past few weeks. The investigation broke wide open on Wednesday, with the release of emails and text messages that suggested Kelly arranged the traffic jams to punish Fort Lee's mayor for not endorsing Christie for re-election. The gridlock delayed emergency vehicles, school buses and countless commuters for four days. In other developments in the case: The chief federal prosecutor in New Jersey, U.S. Attorney Paul Fishman, said he was "reviewing the matter to determine whether a federal law was implicated." The Legislature is also investigating. Using public resources for political ends can be a crime. David Wildstein, a former Christie appointee who resigned from the Port Authority of New York and New Jersey after being implicated in the scandal, refused to answer questions Thursday from the legislative committee that is investigating. Besides firing Kelly, the governor asked his former campaign manager Bill Stepien to withdraw from a bid to become the next state GOP chairman. He said he was disturbed by the "callous indifference" displayed by Stepien in the emails released Wednesday. Stepien had widely been seen as a potential campaign manager for Christie if he runs for president. At the news conference, Christie said he planned to go to Fort Lee on Thursday to apologize to Mayor Mark Sokolich in person. Sokolich accepted Christie's news-conference apology but urged the governor to delay his visit, saying he suspects the whole story has yet to come out. The mayor said the emails and text messages revealed that the governor's office was tainted by "venomous, petty" politics. The allegations turned a local traffic furor into a national issue and raised new questions about the governor's leadership and integrity as he lays the groundwork for a White House bid. "I had no knowledge or involvement in this issue, in its planning or execution," he said of the lane closings. And I am stunned by the abject stupidity that was shown here. Christie focused repeatedly not on the lane closings themselves but on how upset he was that his staff didn't tell him the truth when asked, saying he was "heartbroken" and "betrayed" by his tight-knit circle of advisers. He said he saw the emails and text messages for the first time on Wednesday, and was "blindsided" by what he read. "What did I do wrong to have these folks think it was OK to lie to me?" he asked. Kelly hasn't commented. Christie said he hadn't spoken to her since the emails were released, saying he didn't want to be accused of trying to influence a possible witness. "Time for some traffic problems in Fort Lee," Kelly wrote in August in a message to Wildstein. For weeks, Christie had asserted that the closings were not punitive but part of a traffic study. On Thursday, he acknowledged that was a lie, because his staff didn't tell him what it had done. At the same time, he said: "I am responsible for what happened. I am sad to report to the people of New Jersey that we fell short. Associated Press writer Steve Peoples in Washington contributed to this report.