Why keeping the King safe is Trump's top priority

King Charles's trip to the USA is still going ahead, despite a gunman attempting to storm a dinner attended by President Trump on Saturday night.

It's the first state visit to the country by a British monarch since Queen Elizabeth II in 2007. Charles is also due to emulate his mother by addressing Congress.

Officials from both sides of the Atlantic are working closely on security arrangements. But has the tour been compromised by the assassination attempt? And what does it take to protect a head of state?

Niall speaks to Dai Davies, a former head of Scotland Yard's Royal Protection Command.

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