What is the White House press pool and why is it in a row with Trump?

Image source, EPA Image caption, A network boycott affected live TV coverage of Trump's ribbon-cutting event at the White House

When Donald Trump unveiled a helipad at the White House on Monday, his remarks were barely audible in live footage of the event.

This was due to a row over an institution that rarely makes the news – the White House Press pool.

Yet it is at the heart of relations between the US president and the media, and this dispute could have constitutional implications.

Coverage of upcoming presidential engagements, which include the UN General Assembly in New York, could be affected.

It is a group of news organisations that combine resources to follow presidents wherever they are - in the Oval Office, at state dinners, on Air Force One or on holiday.