Other than a few typos, which I found a bit distracting, this was a sobering look at what many of us feared was going on in the White House. Told in a quite matter of fact way that did not seem to be going for shock value or sensationalism made it all the more believable. Combined with quotes from those he interviewed are the author's own impressions. If given a choice to believe a president who has lied every single day about easily fact checked events, and an author who was seen with a visitor pass on a nearly constant basis by white house reporters, I am more inclined to believe the author than a president who claims he wasn't there. There are a few descriptions of events that have been disputed as inaccurate but I don't think an honest mistake here and there (such as similar names being confused) negate the facts. Perhaps these were due in part to a rush to publish a week or so early in response to an attempt from the president to block the publication.
Considering the president's desperate attempt to block this publication, and considering the author's statement that some of his interviews are recorded. combined with the fact that nobody is disputing the actual quotes, I find it to be believable.