White House press ban - what is the pool and why is it in a row with Trump?

The row over the White House pool affected live TV coverage of Trump's ribbon-cutting event on Monday

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, as well as potentially affecting coverage of the future presidential engagements.

Tensions are high. During Trump's visit to the UN General Assembly in New York on Tuesday, he lashed out at a reporter from CNN - one of the media outlets he has come into conflict with.

What is the White House press pool?

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.

The idea, conceived decades ago, is that having a pool saves on costs and space and it is not practical for hundreds of media outlets to follow the president around.

Members of the pool share their material - pictures and descriptions of the president's movements - with the wider media.

The pool is always on standby in case an event requires the president to speak to the nation.

This latest row centres on the TV pool which has five members - CNN, ABC, CBS, Fox News and NBC.

It 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.

Watch: Mamdani says press allowed at event with Trump regardless of "critique"

Why did US networks pull out of filming Trump?

Fox News Washington bureau chief Bryan Boughton, who currently holds the rotating role covering the White House, wrote in an email seen by the BBC on Monday that "effective today, the TV pool will not be covering events designated as pool coverage" of President Trump.

In a joint statement, the five networks said: "The public has a vital interest in receiving accurate, independent information about its government.

"No administration should restrict a news organisation because it objects to its reporting."

The First Amendment of the US Constitution protects speech and press freedoms.

It forbids the government from "abridging" the freedom of the press - language that courts have traditionally interpreted as preventing the government from discriminating against the media based on the content of their coverage.

CNN, Politico and MS NOW have filed a lawsuit against the Trump administration to "defend the principle that the government does not decide what the press reports". A hearing is scheduled for Wednesday.

In a joint statement on Monday, they said: "Without notice or process, the White House revoked our journalists' credentials because it objected to our reporting.

"Left unchallenged, this threatens press freedom and the public's right to independent journalism free from government interference."

Trump's speech to the United Nations on Tuesday was unaffected by the boycott because it was carried by outlets which are not part of the pool.

But the president's movements to and from his various New York events, which are usually filmed, could be subject to the blackout.

CNN appears to have taken the decision not to run Trump's UN speech live, despite it being made available through official UN sources. It should have been the pool news outlet with the president on Tuesday but is no longer travelling with him since his ban.