They weren't expecting this.
The Guardian ran the first article (link here) about extremely harsh words Bannon used to describe Trump. The most damning arguably was his calling action by Trump's family "treasonous" and "unpatriotic." He labeled Trump himself as "narcissistic" and said any public Congressional hearing would "crack Don Junior like an egg on national TV."
As for Trump's corrupt business practices, Bannon said "this is all about money laundering. Mueller chose [senior prosecutor Andrew] Weissmann first, and he is a money-laundering guy. Their path to fucking Trump goes right through Paul Manafort, Don Junior, and Jared Kushner. It’s as plain as a hair on your face."
Still worse, Bannon said corruption "goes through Deutsche Bank and all the Kushner shit. The Kushner shit is greasy. [Prosecutors are] going to go right through that. They're going to roll those two guys up and say play me or trade me."
Over at New York magazine, they focused on other revelations in the book, specifically how both Trump and his family hoped he'd lose the election last year (link here). His campaign staff were preparing for the same. The worse thing they wanted was to win.
It's difficult to see how Trump will be able to bounce back from all these revelations, particularly given the book isn't even out yet. Almost certainly it will contain more juicy details that will further embarrass the White House.