Donald Trump once called a room full of America’s top generals “a bunch of dopes and babies”, according to a new report.

The 2017 meeting took place in the Pentagon’s secure vault known as “the Tank” — a secure, windowless room apparently viewed within the American military apparatus as sacred — amid concerns among the military’s top brass of “gaping holes in Trump’s knowledge of history, especially the key alliances forged following World War II,” according to an excerpt from a new book due out by two Washington Post reporters.

But, after a lengthy crash course on the rationale behind America’s military presence abroad, and the importance of alliances like Nato, Mr Trump reportedly became frustrated, and snapped at the group that included the former chairman of the joint chiefs of staff, general Joseph Dunford.

"You're all losers. You don't know how to win anymore," Mr Trump said after complaining that the US hadn't won the war in Afghanistan after 16 years.

Mr Trump then continued to muse about the people in charge of America's military, and suggested that they no longer knew how to win wars.

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“I wouldn’t go to war with you people,” Mr Trump reportedly said.

He continued: “You’re a bunch of dopes and babies.”

While the meeting had been previously reported, the outburst had not. And, those newest details show a surprising level of vitriol even for a man known for his penchant for tossing aside the norms of respect and admiration normally associated with the presidency.

In attendance were Gen Dunford and several officials who have now left the federal government, including former Defense secretary Jim Mattis, former National Economic Council director Gary Cohn and former secretary of State Rex Tillerson.

Stephen Bannon, the former chief strategist in the White House, was also there, and described his thinking at the time to the Washington Post.

“Oh baby, this is going ot be f*****g wild,” Mr Biden said he thought after Mr Mattis gave a 20-minute briefing on the power of Nato and America’s “postwar rules-based international order”, as one slide was labelled. Mr Trump has frequently bashed Nato as president, complaining that he does not believe America’s foreign allies are paying enough into the system.

“If you stood up and threatened to shoot [Trump], he couldn’t say ‘postwar rules-based international order.’ It’s just not the way he thinks,” Mr Bannon said.

In the years since, Mr Trump has continued to slam Nato during international trips, and in December made headlines after abruptly leaving a gathering of leaders in London when a video showing Justin Trudeau, Emmanuel Macron and Boris Johnson mocking the American president.