When Donald J. Trump campaigned in South Carolina in December, in a crowded and tightening Republican primary, he made a pointed declaration about one of his opponents, Gov. Chris Christie of New Jersey.

“He totally knew about it,” Mr. Trump told his supporters, referring to the 2013 shutdown of the George Washington Bridge by Christie aides, allegedly to punish a political foe. “They’re with him all the time, the people that did it.”

Mr. Christie, who was not charged, has repeatedly denied such claims. But in a federal courthouse in Newark on Monday, a prosecutor from the United States attorney’s office affirmed Mr. Trump’s view of the scandal, which helped scuttle Mr. Christie’s hopes for the presidency.

The prosecutor, Vikas Khanna, said that the aides, David Wildstein and Bill Baroni, had boasted to the governor about closing several lanes of a ramp connecting Fort Lee to the George Washington Bridge.