What exactly went down during a July 2017 meeting at the Pentagon between President Donald Trump and his military leaders has long been the subject of speculation. One of the tantalizing details that’s been previously reported is that, whatever took place, it provoked then-Secretary of State Rex Tillerson to call his commander in chief “a fucking moron.”

Now an excerpt of a new book published in The Washington Post demonstrates exactly what tipped Tillerson over the edge. An account of the meeting in the upcoming book A Very Stable Genius: Donald J. Trump’s Testing of America depicts Trump becoming increasingly angry as his generals tried to teach him the fundamental basics of American post-war history.

The book states that the meeting took place six months into Trump’s presidency after his generals became concerned about “gaping holes” in Trump’s knowledge of America’s key alliances. The idea was to bring Trump to the Pentagon’s Situation Room, where military leaders, so the plan went, would give him a crash course on who America’s allies were, why they were worth keeping on side, and where on earth they were located.

However, the meeting seems to have descended into chaos almost immediately. Tillerson, then-Secretary of Defense Jim Mattis, and National Economic Council Director Gary Cohn reportedly took turns trying to explain their points to Trump. But Trump is said to have first appeared bored out of his mind before he got increasingly angry.

The account states Trump repeatedly interrupted the lesson after apparently being triggered by a word or phrase uttered by the military leaders. One example given is that he heard the word “base” during the lesson, which sparked him into launching a tirade about how “crazy” and “stupid” it was that the U.S. paid to build and maintain bases overseas.

His first grievance was reportedly against South Korea, when he suggested charging rent for a $10 billion missile-defense system the U.S. built there to protect South Korea and American troops. He then complained about NATO, saying it was in “arrears” to the U.S. for not spending enough money on defense—a complaint he’s repeatedly raised during his presidency.

Trump is then said to have complained about President Barack Obama’s Iranian nuclear deal, and the length of the war in Afghanistan. Each time, his generals reportedly tried to gently explain why his view of these complex geopolitical issues might not be entirely accurate. It was reportedly during a conversation about Afghanistan that Trump blew his top.

The president reportedly called Afghanistan a “loser war,” and told his military leaders: “You’re all losers... You don’t know how to win anymore... I want to win... We don’t win any wars anymore... We spend $7 trillion, everybody else got the oil and we’re not winning anymore.” It’s reported that Trump was so angry at this point that he wasn’t breathing properly.

In his most incendiary comment, Trump—a man who, remember, managed to get out of military duty in Vietnam due to a supposed bone-spur problem—is said to have told the assembled forces, “I wouldn’t go to war with you people... You’re a bunch of dopes and babies.”

The comment reportedly left the room dumbfounded. Tillerson was “visibly seething,” and decided to speak up. The secretary of state said, “No, that’s just wrong... Mr. President, you’re totally wrong. None of that is true.” When the meeting ended soon afterward, Tillerson reportedly stood with a small group of confidants and said, “He’s a fucking moron.”

One senior official summed up the meeting: “We needed to change how he thinks about this, to course correct... They were dismayed and in shock when not only did it not have the intended effect, but he dug in his heels and pushed it even further on the spectrum, further solidifying his views.”

Tillerson reportedly views the meeting as “the beginning of the end” of his time in the Trump administration. He was abruptly fired in March 2018 when he was on a diplomatic mission to Africa to make amends after Trump’s demeaning insults about African countries.

Mattis resigned in December 2018, whereas Joint Chiefs Chairman Joseph Dunford stayed on until September 2019, retiring at the end of his four-year term.