US President Donald Trump declared a national emergency at the United Sates-Mexico border on Friday, a move expected to plunge him into a fight with Democrats over what they call an unconstitutional attempt to fund a wall without approval from Congress.
Trump had demanded Congress include money for the wall, one of his biggest 2016 campaign promises, in a funding bill he signed later on Friday. It was approved overwhelmingly by Congress late on Thursday without the wall money he wanted, a legislative defeat for him.
A national emergency, if not blocked by the courts or Congress, would allow Trump to dip into funds politicians had approved for other purposes to build a border wall.
The spending measure, lacking any money for his wall, is a defeat for Trump in Congress, where his demand for $5.7bn in barrier funding yielded no results, other than a record-long 35-day partial government shutdown that damaged the US economy and his poll numbers.
The measure does include $1.37bn in funding for physical barriers, but no money for concrete walls.
Reorienting his wall-funding quest towards a legally uncertain strategy based on declaring a national emergency is expected to plunge Trump into a lengthy battle with Democrats and divide his fellow Republicans.
The top two Democrats in Congress said they will use "every remedy available" to oppose Trump's declaration.
House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer said on Friday that they will take action "in the Congress, in the courts and in the public".
They called Trump's declaration unlawful, adding that it would "shred the Constitution" by usurping Congress's power to control spending.
Even before the White House announced that Trump would declare an emergency, Republican senators, while sympathetic to his view that the southern border is in crisis, were sceptical of the declaration that would shift funds to the wall from other commitments set by Congress.
"No crisis justifies violating the Constitution," Republican Senator Marco Rubio said on Twitter on Thursday.
Republican Senator John Cornyn told reporters on Capitol Hill he had concerns about an emergency declaration. He said it "would not be a practical solution, because there would be a lawsuit filed immediately and the money would be presumably balled up".
Some Republicans were more supportive of Trump's tactic. "I'm not uncomfortable. I think the president's probably on pretty solid ground," said Republican Senator Richard Shelby.
Fifteen Democrats in the Republican-controlled Senate introduced legislation to prevent the transfer of funds from accounts Trump likely would target to pay for his wall.
Trump said that he will be spending roughly $8bn on border barriers - combining the money approved by Congress with funding he plans to repurpose through executive actions, including the national emergency. The money would come from funds targeted for counterdrug efforts and military construction, but aides could not immediately specify which military projects would be affected.
The funds would cover just part of the estimated $23bn cost of the wall promised by Trump along the 2,000-mile (3,200km) border with Mexico.
The Senate Democrats' bill would stop Trump from using appropriated money to acquire lands to build the wall unless specifically authorised by Congress.
Trump says the wall is needed to curb irregular immigrants and illicit drugs from streaming across the southern border.
But statistics show that irregular immigration has dropped to a 20-year low and that many drug shipments are likely smuggled through official ports of entry, leading critics to argue a wall is not needed.
Reacting to Trump's Friday announcement, Moody's Investment Services said that if funding is diverted from the Department of Defense (DoD) or the US Army Corps of Engineers, "it could have various credit implications for different sectors".
"Diverted funds from the DoD or the US Army Corps of Engineers would negatively impact construction companies with existing contracts with these agencies," said Moody's Assistant Vice President Rebecca Karnovitz.
She also said that "any reallocation of disaster relief funds would be negative for municipalities still recovering from wildfires in California and hurricanes in Texas, Florida and Puerto Rico".