Ever since Rutherford Hayes installed the first White House telephone in 1877, a call from the president of the USA has not been something to be taken lightly.

The phone would ring. An intermediary – often a national security advisor – would ask the recipient of the call to “hold for the president” before the president was put through. Immediately after the call, staff would provide “readouts,” detailing what had been discussed. Even Barack Obama, the first president of the smartphone era, was persuaded to change his usage to fit the White House mould.

In his phone habits, as with so many aspects of his leadership, Donald Trump has broken decisively with tradition. He wields his iPhone just as he did in civilian life, relentlessly and with little thought of protocol or security. Friends, acquaintances, world leaders, journalists, golfers and people he has just seen on television are all liable to get a call out of the blue from Trump’s personal mobile phone.