The monumental traffic jam at the foot of the George Washington Bridge was never supposed to be Gov. Andrew M. Cuomo’s problem.

“I don’t know anything more than basically what has been in the newspaper, because it was basically a New Jersey issue,” Mr. Cuomo told an interviewer in December 2013, as though his curiosity stopped at the state line. His comment came three months after aides to Gov. Chris Christie of New Jersey closed two of the three access lanes to the bridge in Fort Lee, N.J., apparently to punish a mayor who had declined to endorse Mr. Christie.

As the federal trial of two of Mr. Christie’s allies in the bridge scandal churns toward a verdict, however, the Hudson River has not proven to be an especially effective moat.

Trial testimony has suggested that Mr. Cuomo, a Democrat, worked with Mr. Christie, a Republican, to manage the fallout from the lane closings, as the controversy widened from local headache to national scandal — perhaps, as some longtime observers of the two governors have said, to protect Mr. Christie’s re-election bid that year and to buoy Mr. Cuomo’s own the next. (Mr. Cuomo’s aides have denied he participated in any cover-up.)