A former New Jersey official on Friday claimed Governor Chris Christie knew about politically motivated traffic jams as they happened, re-igniting a political scandal that has taken a toll on the prominent Republican.

The letter from a former official at the agency that oversees the busiest U.S. bridge sparked a quick response from Christie, who again denied wrongdoing, and prompted a top New Jersey newspaper to suggest the governor could face impeachment.

David Wildstein, who resigned his Port Authority post late last year, said in a letter that he had proof of the “inaccuracy” of some of Christie’s statements about the so-called “Bridgegate” scandal, which polls show has already started to weigh on Christie’s potential 2016 White House bid.

Since the scandal first came to light, Christie has denied knowing the cause of the George Washington Bridge lane closings, which occurred after the mayor of Fort Lee declined to endorse the governor in a re-election bid and caused four days of massive traffic jams in that city.

“It’s the first time a high-level official has contradicted the governor,” said Julian Zelizer, a Princeton University history professor who specializes in presidential politics.

The letter does not indicate that Christie orchestrated the closures in any way, does not specify exactly when he became aware of the jams, and offers no evidence to back up the claim.

“Mr. Wildstein contests the accuracy of various statements that the governor made about him and he can prove the inaccuracy of some,” the letter said.

Wildstein and Christie attended Livingston High School at the same time, but Christie, a former federal prosecutor, has denied knowing Wildstein well.

One key question is exactly when and how Christie learned of the closures, said Fort Lee Mayor Mark Sokolich, a Democrat.

“There aren’t enough facts. I’m not rooting for him to know or not to know. I will tell you, I remain very, very concerned about it,” Sokolich told CNN. “If it was known at the very tail end, possibly, I’m not sure what this letter means at all.”

‘SMOKING GUN’?

The key question, Zelizer said, is whether Wildstein can produce “smoking gun” evidence proving Christie’s knowledge of the events. State Democrats probing the scandal are likely to jump on that vulnerability, Zelizer added.

The Newark Star-Ledger, one of New Jersey’s largest newspapers, which endorsed Christie in his 2013 re-election bid, posted an editorial after the New York Times first reported about the letter, saying that if the accusations are true, the governor must resign or be impeached.

“Because it will show that everything he said at his famous two-hour press conference was a lie,” the editorial said.

The paper had not endorsed Christie’s initial run in 2009.

The Democratic National Committee, already targeting Christie, who won re-election in a landslide last November, as its greatest threat in the 2016 presidential election, was quick to pounce.

“He’s repeatedly said that he had no knowledge of the lane closures,” said Mo Elleithee, a DNC spokesman. “Today’s revelations raise serious questions about whether that is true.”

Polls taken since the emails emerged early this month showing Christie’s now-fired deputy chief of staff, Bridget Anne Kelly, calling for “traffic” in Fort Lee, show Christie’s popularity slipping in theoretical 2016 White House and primary matchups.

“If we assume it’s true, then we’re in the realm of an outright lie on the part of the governor, and that changes the entire story,” said David Redlawsk, a New Jersey pollster. “It’s the cover-up that gets you.”

As for Wildstein, Redlawsk said, “It very much sounds like the message is quite clear to the U.S. Attorney’s Office: Tell us what you need, and we’ll cooperate.”

The scandal has tarnished Christie’s reputation as a politician ready to reach across the aisle at a time when partisan gridlock has defined Washington.

Christie bolstered his image as conciliator in 2012 when he walked beside President Barack Obama along the storm-hit New Jersey coastline after Superstorm Sandy, in the final months of the 2012 presidential campaign – a move that some supporters of Republican contender Mitt Romney said hurt their party’s chances of retaking the White House.

In the marathon January 9 press conference, Christie repeatedly apologized for actions he blamed on his aides, expressed his shock and said: “I am who I am, but I am not a bully.”

(Writing by Scott Malone; Editing by Gunna Dickson)