One of the defendants in the George Washington Bridge lane-closing trial took the stand Monday.

Bill Baroni, a former executive with the Port Authority of New York and New Jersey, began testimony Monday. He and Bridget Kelly, New Jersey Gov. Chris Christie's former deputy chief of staff, are in the fifth week of their fraud and conspiracy trial.

They face up to 20 years in prison on the most serious charge.

They're alleged to have concocted the lane closures to create traffic gridlock to punish the Democratic mayor of Fort Lee for not endorsing Christie, a Republican, in 2013.

Both defendants contend David Wildstein, a former subordinate of Baroni's at the Port Authority, conceived and carried out the scheme. Wildstein has pleaded guilty and has already testified at the trial.

Baroni, an attorney and former New Jersey state lawmaker, was appointed by Christie in 2010 to serve as deputy executive director of the Port Authority, the powerful bistate agency that operates New York-area bridges, tunnels, ports, airports and the World Trade Center.

Monday's testimony constituted Baroni's first public comments on the case since he made a statement in May 2015 after his indictment.

Wildstein testified earlier in the trial that Baroni and Kelly were active participants in the scheme to punish Fort Lee Mayor Mark Sokolich for his decision not to endorse Christie's re-election bid in 2013. Christie wound up winning by more than 20 points at a time when he was considered a potential top Republican presidential candidate.

According to Wildstein's testimony, during a Sept. 11, 2013, memorial event at the World Trade Center, Baroni told Christie about the traffic jams and of the conspirators' efforts to ignore Sokolich's pleas for assistance, on a day when the gridlock was bringing traffic in Fort Lee to a standstill.

Patrick Foye, the Port Authority's executive director and an appointee of New York Gov. Andrew Cuomo, testified for the prosecution that Baroni twice urged him to close the lanes again after Foye had ordered them reopened on Sept. 13.

Baroni told him the closures were "important to Trenton," Foye testified, which Foye took to mean the governor's office. Christie, who hasn't been charged, has denied knowing about the scheme beforehand or during, and said in response to Wildstein's testimony about the Sept. 11 event that he wouldn't have found it extraordinary to hear about traffic jams at the bridge, considering it is the busiest crossing in the country.

Wildstein also testified Baroni and Kelly participated in a system of political back-scratching in which the Port Authority was used as a "goody bag" of political favors aimed at persuading Democratic lawmakers to endorse Christie.