They are both of an age when, frankly, one might expect a little more grown-up behaviour.

But this week, Donald Trump and Bill Clinton, both aged 70, could not avoid getting into an online battle over the outcome of the election and the pain it caused the former president’s wife.

After Mr Clinton told a local newspaper in New York state that he thought the President-elect, “doesn’t know much”, Mr Trump responded via his favourite communication platform - Twitter.

“Bill Clinton stated that I called him after the election. Wrong, he called me (with a very nice congratulations),” Mr Trump said.

A few minutes later, he followed up with: “He ‘doesn’t know much’…especially how to get people, even with an unlimited budget, out to vote in the vital swing states ( and more). They focused on wrong states.”

Why Donald Trump deserves trust, respect and admiration

Mr Trump appeared to have been angered by an article that appeared in the Bedford-Pound Ridge Record Review, in which editor Ed Baum recounted a recent encounter with the 42nd president in a book store in the town of Pleasantville, near the Clintons' home in Chappaqua.

Mr Baum wrote that Mr Clinton had put the blame for his wife’s defeat on the actions of FBI Director James Comey, and his revelation that the agency had reopened its probe into Ms Clinton’s use of a private email server.

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He said that he had received a call from Mr Trump in the days after the election and that the New York tycoon was cordial “like it was 15 years ago,” when the Clinton and Trump families socialised. Yet he also said he believed

“One thing he does know is how to get angry, white men to vote for him,” he reportedly added.

Mr Baum told The Independent that he had little to add to the account of meeting with Mr Clinton, except to say that the former president had held court in front of about 10 people for 30 minutes. He said that he appeared “relaxed”.