Nobody is more stunned about the stratospheric sales of “Fire and Fury” than the guy who wrote it.

Michael Wolff and I were talking backstage prior to his gig on Tuesday night at the Free Library of Philadelphia, and he confessed that he never saw it coming. He was convinced that he’d gotten the inside skinny about Trump’s den of dysfunction, but in our info-saturated ecosystem, with Trump under scrutiny 24/7, who could have envisioned 11 printings within 12 days of release?

The best explanation is also the simplest: Trump confirms the book on a daily basis.

After hanging out in the West Wing for nine months (“I was let in without anyone weighing the meaning or consequence of what I was going to do,” he said on stage last night) – Wolff concluded in his book that Trump is dangerous, incompetent, ignorant, and unfit to serve.

“Everyone, in his or her own way, struggled to express the baldly obvious fact that the president did not know enough, did not know what he didn’t know, did not particularly care, and, to boot, was confident if not serene in his unquestioned certitudes,” Wolff said. “I was just the guy listening, occasionally nodding my head as if in agreement, and over time, they poured their hearts out.”

Wolff has taken heat for declaring that his book “rings true” despite some material that isn’t true — indeed, there are errors (which he acknowledges), such as getting some names wrong and misstating the year that John Boehner quit the House — and I suggested to him on stage that it would behoove him and his publisher to correct those errors in subsequent printings. But nobody, aside from the deluded Trumpkins, can dispute his portraiture. It “rings true,” because we know with our own eyes and ears that it is.

But Trump is the book’s best salesman. Earlier this week, his doctor announced that his health is fabulous in every respect, and said that Trump is 6-foot-3. In previous years, Trump has often been described as 6-foot-2, but, by giving him an extra inch, Trump’s reported weight no longer qualifies as obese. Sure enough, midway through Wolff’s book, he writes that Trump in the past has “lied about his height to keep from having a body mass index that would label him as obese.”

Ezra Klein, the journalist who founded Vox, says: “The picture painted of Trump in Wolff’s book is the same picture painted of Trump by Trump’s own tweets, speeches, comments, and actions.” The last nine days — which have included Trump saying a vile racist remark, canceling a trip to London because he feared hostile crowds, tweeting that he was a “very stable genius,” and opposing a key national security bill his administration supported after “Fox & Friends” criticized the bill — have been a classic illustration, fattening Wolff’s wallet. What follows is only a partial list:

There was much more, of course — not including the reports that candidate Trump was blackmailed in 2016 by a porn star with whom he’d canoodled a year into his marriage to Melania. That kind of thing doesn’t even tilt the shock meter anymore.

I asked Wolff whether he believes (based on the aggregate info he got from White House insiders) that Trump is just crazy — or crazy like a fox. He said that Trump is too stupid to be Machiavellian, too impulsive to be calculated. There is no grand master plan. There is only the present moment.

There will be many more books in this vein — conservative commentator David Frum’s “Trumpocracy” is brand new, and deserves not to be buried by the Wolff avalanche — and they could help stoke a massive electoral backlash, a blue tsunami in the November midterms. The tea leaves are propitious. Tuesday night, there was a special state Senate election in a rural Wisconsin district where 59 percent of the 2016 voters supported Trump, and where the most recent Republican state Senate incumbent triumphed with 63 percent. This time, the female Democratic state Senate candidate stunned the GOP, winning the rural-red district by nine points.

Timing is everything, in journalism as well as politics. Wolff has caught the wave.

Dick Polman is the national political columnist at NewsWorks/WHYY in Philadelphia (newsworks.org/polman) and a “Writer in Residence” at the University of Pennsylvania. Email him at dickpolman7@gmail.com.