In the absence of any further explanation or elaboration from the White House, there are many questions about the practicality and legality of such a move.

It is not clear whether an executive order has been drafted and if so, when the president intends to act.

It seems certain that there will be an immediate legal challenge and political furore. Mr Trump's critics are saying it is an attempt to detract from the failings of his administration’s response to Covid-19, while his supporters are welcoming the move as necessary to protect Americans.