"I’m not out here to criticize Michael, but I think Michael used flourish-- I’ll put it-- on the events I described," he said in an interview with ABC News’ “The Briefing Room" Thursday.
"'If you can get this idiot elected twice,' Nunberg marveled, you would achieve something like immortality in politics," Wolff writes of Nunberg. ABC News has obtained and reviewed copies of the book ahead of its release.
"I’m from New York and I’m very sarcastic," Nunberg said of the comment, adding that he had not seen that portion of the book yet. "I certainly probably said that but he’s by no means an idiot, at all."
"I’m sure he’s used very colorful words about me in the past," he said of Trump.
In another section of the book, Wolff writes that Nunberg struggled to explain the Constitution to Trump.
“I got as far as the Fourth Amendment before his finger is pulling down on his lip and his eyes are rolling back in his head," Wolff writes of Nunberg's recollection.
Nunberg said the exchange was part of preparations for a GOP presidential primary debate.
"I wasn’t there to teach the president the Constitution. The President had a granular understanding of the Constitution, it was good enough," he said. "It was around eight days before the first debate and I didn’t want him to have any gotcha questions."
The White House has disputed the veracity of Wolff's reporting. Charles Harder, a personal attorney for the president, has sent cease-and-desist letters to Wolff, his publisher and Steve Bannon.
Nunberg declined to dispute the direct quotes Wolff has attributed to him, and also called the author a "good friend."
"When I sat with Michael, who I like a lot, these were very casual type conversations and dinners and lunches," he said. "I’m not disputing what he writes in the totality, I’m just trying to give it a little more color.”
Henry Holt, the book’s publisher, said Thursday afternoon that it now plans to release “Fire and Fury” on Friday, rather than next week “due to unprecedented demand.”