President Trump has confirmed he will use emergency powers to build a wall on the US border with Mexico, saying “walls work”.
Building the wall was a key pledge of Mr Trump’s campaign, but Democrats have described the emergency as a “gross abuse of power”.
He is due to sign the plan along with a spending bill aimed at preventing a repeat of a recent government shutdown.
He announced the plan after Congress refused to pay for a wall in the bill.
However, senior Democrats said immediately that they would challenge the move in the courts.
The declaration will give Mr Trump access to billions of dollars for his project.
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What did Mr Trump say?
Making the announcement to journalists in the White House Rose Garden, the president said the emergency would allow him to get almost $8bn for the wall.
The money is expected to be diverted from military construction projects and efforts to fight the drugs trade.
This is still considerably short of the estimated $23bn cost of the wall along almost 2,000 miles (3,200km) of border.
Can Congress stop Trump’s emergency move?
The National Emergencies Act contains a clause that allows Congress to terminate the emergency status if both houses vote for it – and the president does not veto.
With a comfortable majority in the House, Democrats could pass such a resolution to the Senate. The Republicans control the Senate, but a number of Republican senators have been vocal in their unease about the president invoking a national emergency.
The dissenting Republicans include 2012 presidential contender and new senator for Utah Mitt Romney, Florida senator Marco Rubio, and the senator from Maine Susan Collins, who said the move was of “dubious constitutionality”.
The resolution would however still require Mr Trump’s signature to pass, allowing him to veto it. A supermajority in both houses of Congress is needed to overturn a presidential veto.