The issue at hand is small, even for local politics: the sudden closure, over four days, of a pair of access lanes from Fort Lee, N.J., onto the George Washington Bridge into New York.

But in this traffic mystery, Democrats see a potential scandal that could permanently harm Republican Gov. Chris Christie, who has been riding high as a prospective 2016 presidential candidate.

In September, two of Christie’s top appointees at the Port Authority of New York and New Jersey ordered the lanes abruptly shut to traffic, causing days of gridlock in Fort Lee. Democrats allege that the move was political retribution against the town’s mayor, Mark Sokolich (D), for not endorsing Christie for reelection this year.

With Democratic legislators and the news media continuing to dig up e-mails and other evidence, the two appointees involved in the lane closure have resigned.

Christie has claimed no advance knowledge of the incident and has denied any wrongdoing on the part of his administration. But that has not kept Democrats here and in Washington from pouncing.

New Jersey Gov. Chris Christie told a private audience that the right candidate can overcome party divisions. We wonder who he has in mind? (Casey Capachi/In Play/The Washington Post)

The goal is to puncture the image Christie has carefully cultivated since 2012’s Hurricane Sandy as a bipartisan bridge builder and trustworthy, if pugnacious, executive. His detractors say the episode reveals Christie as what they say he really is — a nasty and corrupt New Jersey politician who bullies those standing in his way.

“It undercuts his key argument that he’s a straight shooter,” said Democratic National Committee spokesman Michael Czin. “It highlights the worst about his bombast and his condescension.”

In interviews here this week, one Democratic leader said the “Bridge-gate” episode reveals the Christie administration’s “Nixon-like dirty tricks,” while another likened it to Watergate. A third speculated about impeachment.

The DNC and other Democratic groups have jumped in with videos and graphics attacking Christie. One of the groups is Correct the Record, a new effort by the American Bridge super-PAC to defend Hillary Rodham Clinton and target her potential GOP opponents if she runs for president.

George Norcross III, an influential Democratic figure in South Jersey and a sometime Christie ally, said Democrats should “be focusing on their own candidates and their own profile.”

“If I was a national Democratic leader, I’d be pretty concerned about circumstances involving the implementation of Obamacare right now versus trying to speculate as to who might be the Republican nominee in a number of years,” Norcross said.

Here in Trenton, the charge has been led by state Senate Majority Leader Loretta Weinberg (D), a 78-year-old widow who has been among Christie’s most aggressive and indefatigable opponents. (After Christie once urged reporters to “take the bat” to Weinberg, the senator displayed two mini Louisville Sluggers on her office mantel — a smaller bat engraved with Christie’s name and a bigger one engraved with hers.)

“Do I think Governor Christie called the Port Authority and said, ‘Close lanes!’? No,” Weinberg said. “But do I think he’s helped to create an atmosphere where his political operatives think they’re free to use the biggest bridge in the world for punitive action against somebody? I have to believe that it has to do with politics, because there is no other rational explanation for it.”

Christie’s advisers expect the controversy will be short-lived, but they said they are prepared to defend him by pointing to his record fighting political corruption as a U.S. attorney.

Still, the bridge incident has invited weeks of public scrutiny of Christie’s administration, including the depths of his political patronage at the Port Authority, which has a multibillion-dollar budget bigger than that of many states.

“The Port Authority has been a haven of patronage under this present administration, much more so than the previous governors have used it,” said Republican former state senator William E. Schluter, who is regarded as a champion of government ethics.

The two officials who resigned were political intimates of Christie. Bill Baroni, a former state senator and rising Republican star, served as deputy executive director at a salary of $290,000, while David Wildstein, a high school friend of Christie’s and a former mayor of their home town of Livingston, made $150,000 per year as director of interstate capital projects. A 2012 profile described Wildstein as Christie’s “eyes and ears within the byzantine agency.”

A senior aide to Christie, who requested anonymity because of the sensitivity of the situation, said Wildstein’s relationship to Christie has been “overstated.” The aide said that the governor’s closest ally at the Port Authority is David Samson, whom Christie appointed as chairman of the Board of Commissioners.

Wildstein ordered the lane closure beginning Sept. 6. Bridge workers later testified at the state legislature that they went along with the plan because they feared for their jobs if they turned on Wildstein, who was seen as carrying out the governor’s wishes.

Officials initially claimed the lanes were closed as part of a traffic study, but no evidence has surfaced to support that explanation.

“It was a juvenile high school prank orchestrated by a high school classmate of the governor’s,” said state assemblyman John S. Wisniewski (D), who has led the legislative probe as chairman of the assembly transportation committee.

Wisniewski, a former state party chairman, drew a comparison to “The Sopranos,” the HBO drama about a New Jersey mobster. The bridge incident, he said, reveals the “bizarre, bare-knuckled tactics” of Christie and his “loyal pitbull” appointees.

Initially, Christie tried to brush aside any suggestion that he had anything to do with Fort Lee’s traffic nightmare. “Unbeknownst to everybody, I was actually the guy out there,” Christie joked at a Dec. 2 news conference. “I was in overalls and a hat. . . . I was the guy working the cones.”

But by last week, Christie appeared to be taking the matter far more seriously. He installed Deborah Gramiccioni, a former federal prosecutor, to take over for Baroni. And he fielded questions from reporters for about an hour, declaring, “We’re going to turn the page now.”

Democrats are determined not to let that happen.

“Welcome to the world that is 2016,” said Adrienne Elrod, communications director for Correct the Record. “We’re watching every word that comes out of his mouth. . . . He’s been able to enjoy for the most part being a pretty popular governor, but he’s never really been tested on the national stage.”

Fresh off a landslide reelection victory in a heavily Democratic state, Christie is the newly installed chairman of the Republican Governors Association and intends to campaign across the country next year for fellow governors.

Many Democratic strategists view Christie as the most serious potential threat to Clinton, saying their imperative is to bloody him up at every opportunity.

“You’ve got the DNC, some of the Hillary-tied PACs diving into this story,” said Kevin P. Hagan, a New Jersey-based Democratic strategist. “You don’t want to continue to give your perceived opponent a pass.”

In Trenton, Wisniewski has subpoenaed more internal e-mails and documentation, promising additional hearings aimed at showing whether Christie or any top officials in his office were involved in the decision to shut down the traffic lanes. “We’re not done,” Wisniewski said.

In Washington on Monday, Sen. John D. Rockefeller IV (D-W.Va.), chairman of the Commerce, Science and Transportation Committee, called for a “comprehensive investigation” of the lane closures. He said the incident “exacerbates my concerns with the governance and previous oversight of the Port Authority.”

A senior aide to Christie acknowledged privately that scrutiny of the governor intensified almost overnight after his easy reelection last month. As the front-runner for the GOP nomination, Christie “fully expects” the scrutiny from Democrats and the news media to continue, the aide said.

As Christie told reporters at his Dec. 2 news conference, “We’re not in Kansas anymore, Dorothy.”