(Reuters) – The Democratic Party plans to launch a political ad on Monday marking the one-year anniversary of “Bridgegate” to remind voters of the scandal that ensnared top aides of Republican New Jersey Governor Chris Christie, a likely 2016 White House contender.

During four days last September, access lanes to the George Washington Bridge, the busiest span in the United States, were abruptly shut down by Christie allies, apparently to punish a Democratic mayor who declined to endorse the governor’s re-election bid.

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The lane closures, which transit authorities first tried to justify as part of a traffic study, caused massive delays for commuters, school buses and emergency vehicles in the borough of Fort Lee, New Jersey, and across the bridge in New York City.

Christie adamantly denied any knowledge of the scheme, and the prominent Republican has sought to distance himself from the scandal as he considers a possible run for the presidency.

The Democratic National Committee said it will seek to renew attention to the bridge lane closures by unveiling a 15-second mobile phone ad called “Gov. Chris Bridgegate Christie.”

The ads will use “geo-targeting” to direct automated calls to voters living on either side of the bridge in northern New Jersey and across the East River in upper Manhattan.

“Gridlock,” the ad begins, according to a transcript. “That’s what happened one year ago in Fort Lee, when the Christie administration shut down lanes to the George Washington Bridge. But it’s also what Chris Christie has brought to New Jersey — wrecking our economy and losing our trust.”

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Christie’s office did not immediately respond to a request for comment.

The traffic study initially cited by the Port Authority of New York and New Jersey as the reason for the lane closures late proved a bogus explanation amid media probes.

In January, a trove of leaked emails indicated an official in Christie’s administration along with one of his Port Authority appointees had ordered the shutdown as retribution against Fort Lee Mayor Mark Sokolich, who refused to endorse Christie’s re-election campaign.

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Christie fired the aide and her supervisor, and the scandal led to the ouster of several Christie appointees at the Port Authority.

An investigation commissioned by Christie’s office earlier this year and paid for by New Jersey taxpayers said neither the governor nor any current member of his staff were party to a lane shutdown plan. Separate state and federal probes also are under way.

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(Reporting by Victoria Cavaliere; Editing by Steve Gorman and Eric Walsh)