The former Vice-President, who has mostly held back from criticising the current administration, called Mr Trump’s behaviour bizarre and said he did not understand governance.

Addressing a bipartisan event alongside Ohio’s Republican governor John Kasich, the respected Democrat claimed 14 leaders had contacted him to try to understand better the actions of the president.

Citing the moment when Mr Trump shoved aside Duski Markovic, the prime minister of Montenegro, at a Nato summit in May and then stuck his chest out and his chin, Mr Biden said one unnamed European leader likened Mr Trump’s stance and body language to Il Duce.

Mr Biden’s imitation of Mr Trump’s behaviour drew laughter at the University of Delaware audience, prompting him to caution: “Not a joke. Not a joke. That’s what people are thinking. That’s what people are thinking”.

Mr Biden, 74, gave examples of Mr Trump’s actions, such as dismissing Rex Tillerson’s diplomatic efforts over North Korea . Violating the norms of personal conduct generates more anxiety and fear than any policy prescription that this President has enunciated, he added.

Sending his secretary of state to talk with North Korea and saying he’s on a fool’s errand it is absolutely bizarre. This is bizarre conduct, he said.

We have a President who does not understand governance.

Mr Biden went on to criticise the president’s use of Twitter and his habit of going on the attack over every little issue.

He said: This penchant for self-aggrandisement and this penchant for tweeting, this penchant to focus so specifically and eternally on what he does or doesn’t do, even if he was right about everything, is sending a message to all of you and sending a message to your younger siblings that is just totally inappropriate.