Almost every week, there's a new book about the Trump White House. But Bob Woodward's book is in a category of its own.

"Fear" came out on Tuesday. And it is already one of the top selling books of the year -- not just on the politics shelf of the bookstore, but in the entire store.

On Wednesday, Barnes & Noble said "Fear" has had the "fastest sales for an adult title since Harper Lee's 'Go Set a Watchman' was released in July 2015."

The bookseller called the pace of sales "phenomenal" and "amazing."

Also on Wednesday, Woodward's publisher Simon & Schuster announced that more than 750,000 copies of "Fear" have been sold as of Tuesday, the first day it went on sale.

The staggering figure includes pre-orders, first day sales of the print copy, ebooks and audiobooks, according to the company. President Jonathan Karp called "Fear" a "cultural phenomenon."

The publisher is trying to keep up with demand, but there are some big backlogs to obtain a hardcover copy.

It's a testament to the widespread interest in, and concern about, the Trump presidency. Woodward's book describes a dysfunctional White House where some of Trump's own aides think he is a danger to national security.

The only similar book that has sold as well as "Fear" this year is "Fire and Fury," which painted a similarly disturbing portrait of the president.

On Amazon, "Fear" is the No. 3 overall top seller for the year. No. 2 is the "Last Week Tonight" parody of a children's book about the Pence family bunny. And No. 1 is Michael Wolff's "Fire and Fury."

What distinguishes Woodward is his decades of reporting on Washington. He has written or co-written 19 books, including "Fear." So when he sounds an alarm, it's serious.

"I've never seen an instance when the president is so detached from the reality of what's going on," Woodward said on NBC's "Today" show earlier this week.

On NPR's "Morning Edition," he said people are "underestimating how serious all of this is." He said "people took actions to protect the country because the president wanted to do things like withdraw from a trade agreement in South Korea."

Woodward's media tour is surely helping stoke sales of the book. But what really seemed to help sales are the early leaks from the book and the resulting condemnations from President Trump.

Book critics have quipped that Trump is an effective book salesman, because his angry tweets and denunciations have fueled interest in "Fire and Fury," "Fear" and several other titles this year.

His endorsements of pro-Trump books like "The Russia Hoax" also help with sales -- but not as much as his expressions of outrage do.

In response to the rush of "Fear" pre-orders, Simon & Schuster ordered hundreds of thousands of extra copies. On Monday the company said "we have reprinted six times for a total of seven to meet extraordinary demand -- that will put one million books in print before we've even gone on sale."

Two days later, on Wednesday, the publisher said it was up to nine printings. This will eventually bring the total number of hard copies in print to 1,150,000.

The book is selling well outside the US, as well. It's also No. 1 on online charts in Canada, the UK and Germany. Simon & Schuster said that foreign rights to the book have been sold in 16 countries.