The president of the United States, one of the most protected people on the planet and among the least accessible to the public, would seem to be a long-shot target for a prank caller looking to have some fun.

But US President Trump, who likes to field his own telephone calls and prefers spontaneity to protocol, is a different breed. So on Wednesday, when a radio shock jock and comedian dialled the White House switchboard impersonating a United States senators aide, he found himself in between barely suppressed giggles and off-colour jokes with his producer patched through to Trump on Air Force One.