Donald Trump struggled to read aloud the US constitution, a new book claims.

The incident, according to reporters Philip Rucker and Carol Leonnig, came during filming for an HBO documentary in which living presidents, as well as judges and lawmakers, read from the historic document.

Stumbling over the text, Mr Trump allegedly blamed people in the room for his mistakes and complained: “It’s like a foreign language.”

The revelation, detailed in Mr Rucker’s and Ms Leonnig’s A Very Stable Genius, comes just days after the US president appeared to stumble and slur his way through a scripted address about the Iran crisis.

Among many false claims and exaggerations, Mr Trump told Iran its "campaign of terror, murder, mayhem, will not be 'tolerited' any longer".

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AFP/Getty Donald Trump celebrity president: A decade in two halves Donald Trump and Nigel Farage pose in the golden elevator at Trump Tower on 12 November 2016. Farage was the first British politician to meet with Trump after the election LeaveEUOffical/Twitter Donald Trump celebrity president: A decade in two halves The inauguration of Donald Trump took place on 20 January 2017. Trump's press secretary Sean Spicer boasted that the crowd was the 'largest ever' to witness an inauguration, a claim that was proved not to be true Getty Donald Trump celebrity president: A decade in two halves In his first 100 days as leader, Trump signed 24 executve orders, the most of any president AFP/Getty Donald Trump celebrity president: A decade in two halves One of Trump's most memorable election pledges was to build a wall between the US and Mexico. 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Named after Mr Trump’s self-declared intellectual brilliance, the book, excerpts of which have been published by The Washington Post, reveals his litany of missteps and willingness to break long-standing norms since becoming president in 2017.