Updated at 3:50 p.m. ET

The book that created a rift between President Trump and his former campaign chief executive and adviser Steve Bannon hit the shelves Friday morning, ahead of the original Tuesday release date, despite the president's threat to block its publication.

Michael Wolff, author of Fire and Fury: Inside The Trump White House, told NPR's Kelly McEvers in an interview set to air on All Things Considered Friday afternoon that he "100 percent" stands behind his reporting, which the White House and some of the books' subjects have sharply criticized.

"I am not a hit man," Wolff said. "I'm someone who just found his way into this story of our time and just wanted to tell it as clearly as possible and with as much understanding as possible."

The pushback and legal threats from the White House may have made the book even more popular. Wolff's work went on sale at midnight in at least one Washington, D.C., bookstore and reportedly sold out in less than 20 minutes. It had already reached No. 1 on Amazon's best-seller list.

Wolff's book paints a portrait of a White House in disarray, with an incompetent President Trump at the center.

"I think the two fundamental issues were that Donald Trump doesn't read anything. Let me accent that — anything. Nothing," Wolff told NPR. "If you're working for the president of the United States, that's an odd position because how do you get information to him? That's already a major hurdle. But then there's the second hurdle — that not only does he not read, he doesn't listen. So it becomes from Day 1, the crisis of the presidency: You can't tell him anything."

An example Wolff pointed to was how Trump was obsessed on his first full day in office with disputing facts that his inauguration had been larger than former President Barack Obama's — which was inaccurate. However, Wolff said, "You couldn't say to him, 'That's not true. You shouldn't have said it from the beginning, but now we have to fix it.' He wouldn't read it and you couldn't tell him it because he won't listen to you. It is entirely his reality."

Wolff also describes how the opposing personalities Trump had surrounded himself with were doomed to fail. From his daughter Ivanka Trump and son-in-law Jared Kushner, who held more liberal positions; to chief of staff Reince Preibus, who was a mainstream Republican; to chief strategist Steve Bannon, who represented the far right.

"Each are trying to use their particular leverage and each has leverage with the president. Also, in order to increase their leverage with the president, they were trying to kill each other. In some nearly literal sense, kill each other," Wolff said. "Certainly, Jared Kushner believed that Steve Bannon was leaking — that the information about Kushner's relationship and conversations with Russians, which put him in legal peril, was coming from Bannon. Reince Priebus almost every day of this administration was a guy who was going to be fired the next day."

"This was an organization that was almost, I'd say, in a real sense shattered from the first day," Wolff said.

Wolff detailed the unprecedented access he was given, describing himself as a "fly on the wall" who "sat there, day after day, and talked to whoever was willing to talk to me and was a fly on the wall — or as Nora Ephron used to say, a wallflower at the orgy."

Some of the people in the book have disputed certain quotes and facts Wolff uses ( Wolff's past work has also been criticized), but he reiterated he stands behind it.

"When you write a book like this, people regret what they said to me," Wolff said. "What they say to any reporter who they relax with and they forget who they're talking to. I have sympathy for that and I think the natural response is to say, 'Oh my god, I didn't say it.' But I will tell you, they said it."

He says he entered the reporting process with an open mind and was "willing to think that this unusual figure had a new way to approach things" that just might work. "I feel that that is not the case now, and I saw and learned that everyone around him feels that is not the case. The train will hit the wall."

While Wolff's book is supposed to be about Trump, comments made by Bannon, his now former top aide, has captured much of the media maelstrom this week.

The book quotes Bannon describing a June 2016 meeting at Trump Tower involving Donald Trump Jr., other Trump campaign aides and Russians as "treasonous" and "unpatriotic."

Since excerpts of the book first appeared in New York magazine and The Guardian ran a report earlier this week, the president has been on the attack, saying Bannon has " lost his mind."

On Thursday night, in a tweet, Trump said he authorized "zero access to White House (actually turned him down many times) for author of phony book!" and added that he "never spoke to him for book." Trump went on: "Look at this guy's past and watch what happens to him and Sloppy Steve [Bannon]!"

Trump and the White House have also tried to downplay the influence Bannon had on Trump's win — something Wolff says is undeniable.

"Steve Bannon is responsible for Donald Trump's election. When Steve joined the campaign in August, they were finished — even Trump acknowledged they were finished," Wolff said. But Bannon helped Trump lay up an economic-focused populist message that resonated with many disaffected voters in states like Michigan and Wisconsin that would be decisive in the outcome.

As for the access he was given to the president, Wolff told the NPR that he spent about three hours in total with Trump during the campaign and after his inauguration. A description of the reporting process posted by New York magazine says Wolff conducted more than 200 interviews overall, including with "most members of his senior staff, and many people to whom they in turn spoke."

White House press secretary Sarah Huckabee Sanders said Wednesday that Trump spoke with Wolff only once since taking office and that it was a brief phone conversation, not a sit-down interview. She said most of the interviews Wolff did at the White House were at Bannon's request.

The fallout from the book does seem to have damaged Bannon's credibility with some former supporters, including Rebekah Mercer, the billionaire backer of Bannon's website Breitbart News. Mercer issued a statement to The Washington Post on Thursday, saying, "My family and I have not communicated with Steve Bannon in many months and have provided no financial support to his political agenda, nor do we support his recent actions and statements" — a development that Trump pointed to in a tweet on Friday.

But Wolff predicted we haven't seen the last of Bannon.

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