Donald Trump will bypass congress to build his wall.
President Donald Trump, citing an "invasion" of drugs and criminals, declared a national emergency at the US-Mexico border on Friday to fund construction of his long-sought wall, a move slammed by Democrats as an unlawful "power grab."
Mr Trump's extraordinary step will enable him to bypass congressional opposition and seek to redirect billions of dollars in federal funds to build the wall - delivering on a key election promise to his right-wing base.
"We are going to confront the national security crisis on our southern border and we are going to do it one way or the other," Mr Trump told reporters in the Rose Garden of the White House.
"I am going to be signing a national emergency," said the US leader. "We are talking about an invasion of our country, with drugs, with human traffickers, with all types of criminals and gangs."
Mr Trump's decision to resort to emergency powers - after a bitter standoff with Democrats blocking his wall project culminated in a 35-day government shutdown - has alarmed lawmakers, including in his Republican Party, who warn it sets a dangerous precedent.
The declaration came after the president agreed to a massive bipartisan spending measure that averts the possibility of a second crippling shutdown.
But House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, the Democratic leaders in Congress, immediately denounced a "power grab" by a president "who has gone outside the bounds of the law" to fund his 2016 campaign pledge to build the wall.
New York State's attorney general, Letitia James, announced the first of what were expected to be a slew of legal challenges, warning a national emergency without legitimate cause could create a constitutional crisis, and vowing to "fight back with every legal tool at our disposal."
Mr Trump said he fully expected to be challenged in court - but voiced confidence he would prevail.
"Look, I expect to be sued," he said bluntly. "Sadly it will go through a process and happily, we'll win, I think."
Mr Trump made the declaration based on the 1976 National Emergencies Act after Congress refused to allocate his requested US$5.7 billion for a wall in a spending bill.
The White House says the emergency order empowers it to pull around US$6.6 billion from other sources, mostly already-allocated funds in the Defense Department Budget.
It is a precedent-setting move, said American University Law Professor Jennifer Daskal, adding that the National Emergencies Act had "never been used in that way, for good reason."
Critics of the move warn that it opens the door for other presidents to call on the legislation whenever they fail to get their way with Congress. A frustrated Democratic president might some day invoke the act to get funds to fight ongoing "emergencies" of climate change and gun proliferation.
The White House dismissed this argument, underscoring how a court showdown might proceed.
"This actually creates zero precedent. This is authority given to the president in law already," said acting White House chief of staff Mick Mulvaney.
"It's not as if he just didn't get what he wanted, so he is waving a magic wand and taking a bunch of money."
A real 'emergency'?
Any legal battle will focus on the definition of "emergency."
The emergencies act "does not provide any explicit limitations on what does and does not constitute a national emergency," Daskal told AFP.
Past emergencies used to invoke the act have been immediate threats such as the September 11, 2001 attacks and the 2009 outbreak of swine flu.
Mr Trump said the emergency now is the flow of drugs and violent criminals across the border.
In the abstract, he appears within his rights.
However, said Bobby Chesney, the associate dean at the University of Texas School of Law, "litigation won't be in abstract."
"The pretext issue looms large here," he said in a comment on Twitter.
He was referring to the problem of Trump being able to sell the border wall issue as an emergency after spending two years in a losing political battle for wall funding.
Mr Trump himself appeared to undermine his argument as he announced the emergency on Friday.
"I didn't need to do this, but I'd rather do it much faster," he said.
Land, military issues
Daskal expects border landowners also to sue to protect their property rights.
"A lot of the land that's at issue is not federal land, it's private land," she said.
Chesney points to a challenge over the use of military funds. Defense Department rules say that, even if diverted, construction funds must be for a project that "requires the use of the armed forces."
The wall however, has been cast from the outset as a civilian project.
"That is the main point of litigation vulnerability," said Chesney.
Court challenges aside, the Democratic chair of the House Judiciary Committee, Jerry Nadler, expressed support for a congressional resolution of disapproval to "terminate" Trump's emergency declaration.
Such a move has a chance of passing both chambers of Congress, but Trump would almost certainly veto it.