A confrontation between President Donald Trump and some of America's biggest news organisations has thrown an institution rarely noticed by the public into the centre of a major dispute over press freedom and presidential access.

The White House press pool is a rotating group of journalists responsible for closely following the president and sharing their reporting, photographs, audio and video with a much larger group of news organisations.

The system allows journalists to document presidential activities even when there is not enough space for the entire White House press corps.

But the arrangement has been thrown into turmoil after Trump barred CNN, Politico and MS NOW from the White House.

The three organisations have sued the administration, while America's five major television networks have suspended their participation in White House television pool coverage.

The dispute could affect how Americans and international audiences see and hear presidential events while raising broader constitutional questions about whether an administration can restrict journalists because it objects to their reporting.

WHAT IS THE WHITE HOUSE PRESS POOL

The press pool exists because hundreds of journalists cannot accompany the president everywhere.

Instead, a smaller rotating group represents the wider press corps.

Pool journalists can accompany the president into the Oval Office, aboard Air Force One, during foreign and domestic travel and at events where space is restricted.

They then distribute their material to other participating news organisations.

Separate arrangements exist for television, photographers, print and radio journalists and other categories of media.

For television, ABC, CBS, CNN, Fox News and NBC have traditionally rotated responsibility for providing cameras and other equipment.

The footage can then be distributed across the participating organisations.

This means one network does not need to send its own complete production crew every time the president appears.

The pool is also important because its journalists remain available in case an unexpected national or international event requires the president to speak publicly.

WHY DID THE DISPUTE BEGIN

Trump announced that CNN, Politico and MS NOW would be barred from the White House after accusing them of publishing false and misleading coverage of his administration.

Journalists working for the three organisations subsequently found their White House access restricted.

The outlets say the government excluded them because it objected to their journalism.

Trump has defended the restrictions and accused the organisations of unfair and inaccurate reporting.

The disagreement quickly developed into a wider confrontation between the administration and major American news organisations.

MAJOR TV NETWORKS SUSPEND POOL COVERAGE

The five television organisations involved in the presidential television pool responded by suspending their participation.

ABC, CBS, CNN, Fox News and NBC said they would stop providing television pool coverage for presidential events designated for that system.

The networks argued that allowing the government to exclude one organisation because of its reporting would undermine independent journalism.

The decision effectively removed the normal shared television cameras, microphones and production equipment from some presidential appearances.

TRUMP'S HELIPAD EVENT SHOWED WHY THE POOL MATTERS

The consequences became visible almost immediately.

Trump appeared at the White House on Monday for the inauguration of a new presidential helipad before departing aboard Marine One.

Without the usual television pool equipment, much of the president's remarks were difficult to hear on available live footage.

Some news organisations did not carry the event at all.

The episode demonstrated that the press pool does more than provide journalists with physical access to the president.

It supplies the technical infrastructure that allows presidential appearances to be distributed quickly across television networks and other media organisations.

CNN POLITICO AND MS NOW GO TO COURT

CNN, Politico and MS NOW have filed a federal lawsuit challenging their exclusion from the White House.

The organisations argue that the administration violated their First Amendment rights by restricting access because it objected to their reporting.

They have also raised due process arguments under the Fifth Amendment.

The First Amendment protects freedom of speech and freedom of the press from government interference.

The case therefore raises an important question over whether the government can deny journalists access available to other comparable news organisations based on disagreement with their coverage.

The administration is defending its authority over White House access.

A federal court hearing is scheduled as the organisations seek restoration of their credentials.

WHY THE CASE COULD HAVE CONSTITUTIONAL IMPLICATIONS

Presidents have considerable authority over security and access inside the White House.

That authority does not automatically mean officials can discriminate between journalists based on their reporting.

American courts have previously considered disputes involving White House press credentials and the government's treatment of individual journalists.

The current lawsuit could test the extent to which constitutional protections limit a president's ability to exclude entire news organisations from access granted to other media outlets.

The final legal position will depend on the federal courts.

WHITE HOUSE LAUNCHES TRUMP TV

The confrontation has coincided with the White House launching a 24 hour online video stream branded Trump TV.

The channel is available through YouTube and carries presidential speeches, administration announcements and footage highlighting Trump's activities.

Unlike independent press coverage, material distributed through the White House channel is produced or selected by the administration itself.

That distinction is central to the wider dispute.

Independent journalists can question officials, select what they consider newsworthy and report information that may be critical of the government.

An official White House channel provides the administration's own presentation of events.

UN GENERAL ASSEMBLY COVERAGE CONTINUES

The television pool dispute does not mean Trump's appearance before the United Nations General Assembly will disappear from television.

His formal UN address can be carried through television infrastructure independent of the White House pool.

However, presidential movements and less formal appearances surrounding his New York visit could receive less television coverage if the pool suspension continues.

That could include arrivals, departures and other interactions that would ordinarily be documented by pool journalists.

WHITE HOUSE HAS CLASHED WITH MEDIA BEFORE

The latest confrontation follows earlier disputes between the Trump administration and news organisations.

The White House previously changed the system under which journalists were selected for pool access, reducing the traditional role played by the White House Correspondents' Association.

The administration also restricted Associated Press access to certain presidential events following a dispute over the news organisation's continued use of the name Gulf of Mexico rather than Gulf of America.

The Associated Press challenged those restrictions in court.

Other presidential administrations have also clashed with individual media organisations.

In 2009, the Obama administration attempted to exclude Fox News from a specific pool interview with an administration official.

Other television networks objected and Fox was ultimately included.

The current confrontation is considerably broader because entire organisations have been barred from the White House and the major television networks have responded by suspending their shared pool operation.

WHY THE PRESS POOL MATTERS

The White House press pool is ultimately a practical solution to a simple problem.

Every journalist cannot follow the president into every room, aircraft or event.

A small rotating group therefore witnesses those events on behalf of the wider press corps and distributes the resulting information.

The current confrontation raises a much larger question about who determines which journalists can perform that role.

Trump argues that news organisations he considers dishonest should not automatically receive privileged access to the White House.

CNN, Politico and MS NOW argue that allowing the government to exclude organisations because officials dislike their journalism threatens independent press coverage.

That disagreement is now moving from the White House briefing room into federal court.