TRENTON, N.J. -- Gov. Chris Christie announced the resignation Friday of one of his top appointees amid an escalating probe into whether Christie loyalists deliberately created traffic jams at a bridge into New York City in an act of political retribution. The governor denied the lane closings were politically motivated.

The resignation of Port Authority of New York and New Jersey deputy executive director Bill Baroni comes a day after a state lawmaker issued seven subpoenas to Baroni and other agency officials and the Democratic National Committee tried to link the controversy to Christie, a potential 2016 Republican presidential candidate.

Christie, who is shuffling some staff positions as he begins his second term, painted Baroni's departure from a plum appointment as an expected move, though he also acknowledged the questions about a bridge delay cause a distraction.

"Sen. Baroni offered his resignation and I accepted it, but this wasn't something I hadn't planned already," the governor said. Baroni is a former Republican state senator and insider who was state chairman of John McCain's 2008 presidential campaign and has been Christie's top deputy at the bistate agency for four years.

The issue at play involves the George Washington Bridge, one of the world's most heavily traveled spans. The town on the New Jersey side of the bridge is Fort Lee, whose Democratic mayor did not endorse Christie in his re-election campaign last month. While Christie is a Republican, his campaign focused heavily on bipartisan support to bolster his image as a pragmatic executive who will work with political opponents.

On Sept. 9, two of the three local-access lanes from Fort Lee to the bridge's upper level were closed without warning. Officials at the Port Authority, the agency that operates the bridge, said the closures were for a traffic study. Christie said Friday that he believes that version of events, though he said Baroni and others did not communicate the plan properly. Christie also said he does not believe anyone on his own staff was involved in the lane closures and that he did not know about them until later.

Fort Lee officials said they were not informed of the closures in advance. The closures led to gridlock for four days.