Washington (CNN) Michael Wolff, the author of a new exposé on President Donald Trump's first year in office, claims the 25th Amendment -- which addresses the transition of powers if a president is unable to execute his responsibilities -- was frequently discussed within the President's close orbit.

"This is, I think, not an exaggeration, and not unreasonable to say, this is 25th Amendment kind of stuff," Wolff, author of "Fire and Fury: Inside the Trump White House," said in an interview on NBC's "Meet the Press." He said people in the West Wing brought it up "all the time."

"They would say ... we're not at a 25th Amendment level yet," Wolff said.

In the interview, Wolff did not provide information on the sourcing for his remarks; CNN has not independently confirmed all of the assertions in his book.

The White House has refuted the claims in the book since excerpts of it began to surface online ahead of its publication last week, with press secretary Sarah Sanders calling the book "complete fantasy" and a personal attorney for Trump sending a cease-and-desist letter to the author and publisher.

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