Author Michael Wolff said Friday that former White House chief strategist Steve Bannon went through a "transformation" working under President Trump as he realized his boss was not competent and could not carry out his duties as commander in chief.

"I spoke to Steve as I spoke to many people throughout the length of the reporting here. I really saw a transformation not only of Steve, but of everyone. But Steve in a way is most vivid, or his language is the most vivid," Wolff said on NBC Friday morning.

"The transformation was, 'We thought this presidency could work. We thought Donald Trump is an interesting, unique character and we might be able to do something here.' And they saw him over that time come to the conclusion he cannot do this job," he added.

Wolff's book, titled "Fire and Fury: Inside the Trump White House," was set to be released next Tuesday, but the publisher moved the release day to Friday.

The book has been criticized by the media and White House as one that misstates basic facts.