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.

There are separate pools for TV, photographers and print and radio outlets, as well as a “new media” category.

Material from the TV pool feed is shared between its members – CNN, ABC, CBS, Fox News and NBC – to save on costs and space. The pool is always on standby in case an event requires the president to speak to the nation.

The latest row began on Friday, when Trump said he was banning three outlets – CNN, Politico and MS NOW – from the White House, accusing them of spreading “fake news” and “fictions and lies” about his team.

A day later, reporters from those organisations found that their entry badges to the White House had been disabled.

On Monday, all the major US TV networks decided to pull out of White House pool duties – in effect boycotting presidential events.

That afternoon came the first test of this post-pool era – the new helipad at the White House.

With no pool cameras present, much of the media did not carry any pictures and for those that did, there was no microphone to clearly pick up the president’s remarks.

But there were no such problems at Trump’s meeting later that day with New York Mayor Zohran Mamdani, because it was not dependent on pool cameras and lots of media were there.