(Reuters) - Testimony by a former ally of New Jersey Governor Chris Christie that the Republican knew about the “Bridgegate” traffic scandal as it was going on could endanger his best chance at a political future: a role in a Trump administration.

New Jersey Governor Chris Christie reacts to a question during a news conference in Trenton, New Jersey, U.S. on March 28, 2014. REUTERS/Eduardo Munoz/File Photo

Christie has denied claims he had been an active participant in the plan to deliberately create massive traffic jams on a key bridge to New York to punish a Democratic mayor’s refusal to endorse his re-election bid.

But each piece of evidence that ties Christie closer to the scandal makes him more of a liability for Republican presidential contender Donald Trump, a New York real estate developer who has tapped the governor to head his transition team.

“Every revelation increases the odds that Trump will distance himself from Christie, especially as Election Day gets closer,” said Julian Zelizer, a professor of history and public affairs at New Jersey’s Princeton University.

“Christie still serves a value to Trump, who wants to compete in blue states,” he added. “But there will be a point where the revelations overwhelm any sense of loyalty or any perception that he remains valuable to the campaign.”

A Trump campaign spokeswoman did not immediately respond to a request for comment.

The 53-year-old governor’s political future is already limited. New Jersey law prevents him from running for a third consecutive term next year, and polls show that Bridgegate has seriously hurt his popularity, explaining in part why Christie, who hoped to be president, quickly tied his fortunes to Trump.

Christie on Tuesday repeated that he had not known about the lane-closure plan.

“There’s all kinds of stuff going on up in a courtroom in Newark, and I want to be really clear to all of you about something,” Christie told reporters in Trenton. “I had no knowledge prior to or during these lane realignments.”

That contradicted the testimony of David Wildstein, a former executive at the Port Authority of New York and New Jersey, in a federal court in Newark, where two other ex-Christie allies face criminal charges for their role in the scandal.

While Bridget Kelly, his former deputy chief of staff and Bill Baroni, a close associate and former executive at the Port Authority, are on trial for their role in the 2013 incident, Christie himself has not been charged criminally.

The governor was at the peak of his popularity at the time, having stepped into the national spotlight when he toured Superstorm Sandy-ravaged New Jersey shore with President Barack Obama.

With his eye on the White House, he was eager to secure the endorsements of Fort Lee Mayor Mark Sokolich and other Democratic mayors to show he was a politician able to forge alliances across party lines.

The lane closures, which generated massive traffic jams at the George Washington Bridge and national headlines, took a heavy toll on Christie’s image and drew the mockery of the state’s favorite son, rock star Bruce Springsteen.

A Rutgers-Eagleton poll conducted early this month found that 23 percent of state residents held a favorable view of Christie, down 7 percentage points from a year earlier and one-third of what it was at Christie’s peak of popularity in February 2013.

“Bridgegate almost wholly contributed to the downfall that we’ve seen for the governor,” said Ashley Koning, director of the Eagleton Center for Public Interest Polling at New Jersey’s Rutgers University.

His low popularity makes it highly unlikely he’d be successful in another statewide run, whether it was for governor in 2021 or for another office, she said.

After Christie’s bid for the 2016 Republican presidential nomination failed, he pivoted quickly to endorse Trump, who embraced his support and named him transition chair in May.

Christie would be charged with helping build a cabinet for a Trump White House and serve as a liaison with the outgoing Obama team.

Christie was a federal prosecutor in New Jersey, suggesting the likeliest job in a Trump cabinet would be attorney general.

“It’s hard to imagine that he would be able to win Senate confirmation with knowledge of this scheme confirmed,” said Brigid Callahan Harrison, professor of political science and law at New Jersey’s Montclair State University.

Trump could also pick Christie for a staff role, she said. Bill Stepien, who managed both of Christie’s gubernatorial runs, is an adviser to the Trump campaign.

Harrison added: “From what we know of Trump, he may not be overly cautious about affiliating himself with people that could be damaging.”