Get ready: Another ex-Christie staffer is slated to testify Monday on ‘Bridgegate.’

Kevin O’Dowd, New Jersey Gov. Chris Christie’s former chief of staff, was subpoenaed on Wednesday by lawmakers on the New Jersey legislative committee investigating the September 2013 lane closures on the George Washington Bridge. Assuming he appears, O’Dowd will be the highest-ranking Christie administration official so far to appear before the committee – an A-list witness who will have followed a month’s worth of B-list appearances.

If you haven’t been following this story closely, here’s some of what you missed:

Earlier in the week, the committee interviewed Pat Schuber, one of the commissioners of the Port Authority of New York and New Jersey – the sprawling bi-state agency with a $4.4 billion budget that manages bridges and tunnels connecting New York and New Jersey, along with airports and the World Trade Center. Schuber, a former Bergen County, N.J. Republican elected official appointed to the board by Christie, claimed to know nothing about the lane closures.

But like so many witnesses who have appeared before the committee, what is curious is that Schuber wasn’t curious. Once he learned something had gone awry at the agency, Schuber told lawmakers that he decided it was “not something I wanted to be involved with.” Never mind that it hadn’t really become a news story yet (people were still calling the lane closures a traffic study). Schuber never wondered why Port Authority Chairman David Samson might have offered him unsolicited help in responding to a letter from a New Jersey state senator about the matter. Two weeks after the incident, Schuber personally took a 22-minute-long phone call from Fort Lee mayor Mark Sokolich, whose town was jammed up by bridge traffic and who might well have been the target of the operation. Yet even then, Schuber said he never bothered to ask the agency staff what had happened.

Originally, the star of the day was supposed to have been Port Authority executive director, Patrick J. Foye. Appointed by New York Gov. Andrew Cuomo in 2011, Foye was the official who ordered an end to the lane closures in an email sent during the early hours of September 13, 2013. In that message, Foye said he believed that the operation had broken “Federal Law and the laws of both states” and he chastised N.J. Governor Chris Christie’s top appointees for putting lives at risk. In response, the agency’s then-chairman, David Samson, a top Christie fundraiser and confidant and a former N.J. Attorney General, aided the efforts of the agency’s deputy executive director, Bill Baroni, and another political appointee, David Wildstein, to – in Baroni’s words – “retaliate” against Foye.

Foye presumably has a more forthcoming memory than Pat Schuber, and lawmakers (and reporters) are eager to hear from him.

“This isn’t the first time the federal investigation has interfered with the N.J. legislature’s inquiry.” Brian Murphy, msnbc contributor

The trouble is, someone else wants to talk to Foye: Paul Fishman, the U.S. attorney for New Jersey, whose office now has almost ten investigators digging into the lane closures and other Port Authority activities in New Jersey. Fishman wrote to legislators asking them to postpone their hearing with Foye. “His letter was carefully written to reveal nothing,” said one committee member who saw it firsthand.

This isn’t the first time the federal investigation has interfered with the N.J. legislature’s inquiry. In January, lawmakers subpoenaed David Samson, but he refused to comply once the U.S. Attorney sent him a subpoena in March.

Other witnesses – the ones who may know why the lanes were closed to begin with – have all asserted that testifying before the committee or producing documents could put them in legal jeopardy. Gov. Christie’s former deputy chief of staff, Bridget Anne Kelly, who sent the August 13 “time for some traffic problems in Fort Lee” email, and Bill Stepien, Christie’s former campaign manager, both successfully fought off the committee’s subpoenas in New Jersey state courts. David Wildstein, too, asserted his Fifth Amendment rights when he appeared before the committee in January. Meanwhile, Fishman convened a grand jury and interviewed high-ranking Christie administration officials, including spokesman Michael Drewniak and the administration’s top lawyer, Charles McKenna. This is all happening against a larger backdrop of ongoing Securities and Exchange Commission investigations into the Port Authority, as well as a somewhat parallel inquiry being led by Manhattan District Attorney Cyrus R. Vance Jr.

In the absence of A-list witnesses, the committee has been forced to work through a B-list as they try to figure out what motives were behind the lane closures and whether Gov. Chris Christie had any role in the operation’s planning.

“Although Christie is often seen checking email and sending text messages on a handheld device, only one email from him has been made available to the legislative committee, making some on the committee doubt that they have seen all there is to see.” Brian Murphy, msnbc contributor

Their sessions have not been dramatic, yet they have unearthed a better understanding of how Christie’s appointees at the Port Authority interacted with agency staff and the governor’s aides in Trenton. Former staff members in the governor’s Office of Intergovernmental Affairs (IGA), an office responsible for cultivating alliances with local officials in the state’s municipalities, indicated that the governor knew that members of his administration and the manager of his re-election campaign had knowledge of the lane closures even as the he publicly claimed otherwise.

This is where Kevin O’Dowd will come into play on Monday.

Based on the testimony of former IGA officials, Christie’s top aides were made aware of Foye’s email – the one about laws being broken – and the possibility that the governor’s appointees at the Port Authority and other aides in Trenton might have been involved in planning the operation just hours after it was sent out. In October, Christie reportedly discussed the matter with O’Dowd, two months before a press conference where he denied that he or his staff knew anything about it.

O’Dowd is unlikely to point to a smoking gun, but he will be forced to recount his discussions with other administration officials and the governor himself. This may help fill in some blanks. Although Christie is often seen checking email and sending text messages on a handheld device, only one email from him has been made available to the legislative committee, making some on the committee doubt that they have seen all there is to see.

Meanwhile, there is a growing chorus, not only among Republicans, but also among some Democrats, for the committee to wrap up its work. O’Dowd’s appearance was announced on short notice, and is thought to be related to his pending nomination to be the next attorney general of New Jersey.

“It’s an open secret that Sweeney intends to run for governor to succeed Christie and doesn’t want to empower any rivals.” Brian Murphy, msnbc contributor

New Jersey politics isn’t strictly partisan, and Christie’s alliance with Steve Sweeney, the Democratic president of the New Jersey state senate, seems to be at work here. It’s an open secret that Sweeney intends to run for governor to succeed Christie and doesn’t want to empower any rivals, especially Bridgegate committee co-chairman John Wisniewski, a Democratic state assemblyman. Earlier this year, Sweeney was expected to abandon any legislative effort to investigate Bridgegate, but once Bridget Kelly’s “time for some traffic problems” email became public, he had no choice but to let lawmakers pursue their work. Now he wants to get back to laying the groundwork for his campaign, something that involves him returning to an unusually cozy relationship with the governor.

So it’s against that backdrop – tensions between the two parties but also between two men who might be positioning themselves to run for governor in the next election – that Monday’s hearing will be playing out. This story has always been about more than four days of traffic last September.