A US federal appeals court will hear verbal arguments later today (Tuesday, 2300GMT) on the US government's request to overturn a block on President Trump's travel ban.
The hearing was scheduled late on Monday night - just as the justice department filed a briefing arguing that national security was at risk because of the court's intervention.
Thousands of immigrants and refugees affected by the executive order have arrived in America since Friday's ruling to halt the travel ban.
President Trump tweeted late on Monday night that the courts "must act fast".
Harry Horton reports from Washington.
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In just the third week of Donald Trump's young presidency, a legal showdown will take place at an Appeals court, in San Francisco.
At 3pm local time on Tuesday, an hourlong oral argument will take place - unusually, by telephone - over whether to reinstate Donald Trump's controversial travel ban.
The government argues that with the ban temporarily lifted, the nation's safety is at risk.
Here's White House Press Secretary Sean Spicer speaking to reporters on Air Force One.
CLIP
Donald Trump's opponents - led by the states of Washington and Minnesota - and backed up by over one hundred silicon valley tech firms - argue that the President's executive order "unleashed chaos".
Whatever the outcome - the losing side will almost certainly appeal and the case could well end up in the Supreme Court.
Meanwhile Democrats are more determined than ever to disrupt appointments to Donald Trump's skeleton cabinet.
Many heads of departments are yet to be confirmed by the Senate. On Tuesday, Vice President Mike Pence might be needed to cast the deciding vote for Secretary of Education pick Betsy DeVos.
On the Senate floor late on Monday night, Senator Elizabeth Warren made a last ditch attempt to block her nomination.
CLIP
Courtroom showdowns and drama on capitol hill - another regular day in Donald Trump's America.
Harry Horton, Washington.