White House senior policy adviser Stephen Miller attacked a new book about the inner workings of President Donald Trump's White House as "grotesque" and "fiction" in a tense interview Sunday, NBC News reported.

"The book is best understood as a work of very poorly written fiction, and I also will say that the author is a garbage author of a garbage book," Miller said on CNN's "State of the Union."

Miller also lamented Steve Bannon for making "grotesque comments" in the book, ones he said are "so out of touch with reality" and vindictive." He described the former chief strategist's role as "greatly exaggerated" and twice called Trump a "political genius."

The tell-all book, Michael Wolff's "Fire and Fury: Inside the Trump White House," has prompted a swift backlash from Trump and his White House. In the book, Bannon makes a number of scathing critiques against Trump and his inner circle, including calling a meeting between Trump campaign officials with a Russian lawyer in Trump Tower during the presidential campaign "treasonous" and "unpatriotic."

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