New Jersey Gov. Chris Christie was once considered a frontrunner for the Republican nomination in 2016. The Fix’s Chris Cillizza gives his take on how badly Bridgegate will hurt his presidential ambitions. (Video: Jorge Ribas/The Washington Post)

Updated: Former Port Authority official David Wildstein pleaded guilty Friday and implicated Bill Baroni and Bridget Kelly in the scandal, with Baroni and Kelly being indicted later Friday. Given that news, we're resurfacing this explainer from shortly after the incident made national headlines. Not much of substance has changed since, we'll note. Lawyers working for Gov. Chris Christie completed a review that suggested the governor wasn't involved, which wasn't a surprise. A report from the Democratic-controlled state assembly didn't find a link either, but they aren't letting Christie off the hook so easily. The damage is mostly done: Christie's poll numbers since the incident came to light keep sliding downward.

We here at The Fix know that political scandals -- especially those involving Port Authorities and access lanes and traffic studies -- can be more than a little dense. And that goes double when New Jersey's complex world of political fiefdoms is involved.

So here are the basics of the scandal that forced New Jersey Gov. Chris Christie (R) to spend almost two hours taking questions from reporters and has led to the ouster of top aides. Let us know if your question doesn't get answered, and we'll update the post.

So how, exactly, did this get started?

In September 2013, the Port Authority of New York and New Jersey closed two of three local access lanes from Fort Lee, N.J., to the George Washington Bridge, which connects the two states and is the most heavily trafficked bridge in the world. The closures, which lasted four days, created a traffic bottleneck in Fort Lee that has been described as the worst traffic jam since Sept. 11, 2001.

For a great illustration of the above, be sure to click here.

How did it become a political issue?

In the days after the traffic jam, the media began asking questions -- namely why two of three lanes were closed and why the authorities didn't seem to be prepared for the ensuing traffic problems. The Port Authority said, at the time, that it was part of a traffic study. Two weeks later, New Jersey Democrats announced they would be looking more closely into the matter.

Christie was overwhelmingly reelected on Nov. 5, taking 60 percent of the vote. But soon after his victory, Democrats began to allege that the lane closures were politically motivated -- specifically, that Christie's office created the traffic jam as political retribution against Fort Lee Mayor Mark Sokolich (D) for not endorsing Christie's reelection.

Do Democrats have proof of this?

At this point, the only thing that has really been proven is that Fort Lee was targeted for a traffic jam and that both Christie's staff and his appointees at the Port Authority were involved. All of this became clear when communications between Christie's staff and the Port Authority officials were released. The documents, including e-mails and text messages, were turned over as part of the state legislature's investigation into the matter.

The communications do show that Christie's people planned the traffic jam and were overjoyed about Sokolich's problems. But there isn't anything in the public record yet that suggests precisely why Fort Lee was targeted -- be it a lack of an endorsement or anything else having to do with Sokolich.

Why would Christie's office target a Democratic mayor for not endorsing him?

In most states and in most races, a Republican governor would hardly expect a Democrat's endorsement, and certainly wouldn't move to punish one who declined to give one. But this is New Jersey, where the same rules rarely apply. In fact, Christie was endorsed by several Democratic mayors and has a good relationship with some Democratic state legislators, including state Senate President Stephen Sweeney.

Was Christie involved?

To this point, there is no evidence showing Christie knew about or took part in the scheme. Christie has issued strong, blanket denials, including saying: "I had no knowledge or involvement in this issue, in its planning or execution."

Christie also declared: "I am not a bully."

So who was allegedly involved?

Here are the major players:

1. Bridget Anne Kelly: Christie's now-former deputy chief of staff appeared to get the ball rolling by sending an e-mail to a Port Authority official saying, "Time for some traffic problems in Fort Lee." Christie announced her firing in January 2014, eviscerating her conduct and saying she lied to him about her involvement in the lane closures.

2. David Wildstein: He is expected to plead guilty Friday. He was the Port Authority official on the receiving end of Kelly's e-mail, to which he responded: "Got it." From the beginning, he was the Port Authority official who Christie said was behind the "traffic study." An appointee of Christie, he announced his resignation from the Port Authority in early December 2013.

3. Bill Baroni: He was Christie's top appointee on the Port Authority. He resigned a week after Wildstein. Christie said at the time that he had already planned to replace Baroni with someone else but added that Baroni had failed to follow proper protocol in informing local officials about Wildstein's traffic study.

4. David Samson: A close adviser of Christie's, he resigned his position as chairman of the Port Authority in March 2014 but insisted he was headed out the door regardless. Since then, he has emerged as a potential target of the investigation and has had his name removed from the law firm where he practiced.

5. Bill Stepien: He was Christie's campaign manager for his 2013 reelection campaign, but Christie cut ties with him in January 2014, telling him to scrap his plan to run for chairman of the state GOP and to end his consultancy with the then-Christie-run Republican Governors Association.

And what was in these e-mails and texts?

A whole bunch of juicy plotting and ill-advised commentary. Besides the initial exchange between Kelly and Wildstein, there was:

  • Further talk in advance of the lane closures about the "traffic study" that they were preparing.
  • Talking about Sokolich's frustration, an unidentified person said, "Is it wrong that I am smiling?" and added, “I feel badly about the kids . . . I guess."
  • Another person responds, "They are the children of Buono voters," referring to Christie's Democratic opponent in the 2013 campaign.
  • After the Wall Street Journal questioned the lane closures, Christie campaign manager Bill Stepien said, "The mayor is an idiot," and Wildstein added, "It will be a tough November for this little Serbian" -- apparently a reference to the Croatian Sokolich.

Stepien's remarks clearly cost him dearly. Christie said he had no reason to believe Stepien was involved in the wrongdoing, but that his conduct after-the-fact shows a lack of judgment.

So how does this affect/involve Christie?

Christie's problem was initially that he was very dismissive of the scandal, calling it "not that big a deal" and accusing the media of sensationalism. He even joked about moving traffic cones himself. Christie also said that the lane closures weren't political in nature and that he didn't believe his staff was involved.

All of these statements, of course, turned out to be either false or just plain unhelpful. And Christie, for lack of a better phrase, had some 'splainin' to do. Recognizing the tough spot he was in, Christie apologized profusely in January 2014, holding a one hour, 48 minute news conference in which he said the word "apology" or "apologize" 34 times -- along with firing a staff member and sanctioning another top aide.

And while he has not been implicated in any wrongdoing, Christie's approval rating in New Jersey continues to drop to this day -- so much so that his 2016 presidential aspirations seem pretty dim.

The bridge, it seems, has become a metaphor for the formerly high-flying governor's increasingly snarled political fortunes.

Okay, so what the heck is a Port Authority?

Why didn't you ask sooner!?

This is governing body that manages transit -- via bridges, tunnels and air -- in New York City and Northern New Jersey. It is run jointly by the governors of New York and New Jersey and features appointees of both.

This post initially published in January 2014. It has been updated throughout.