The action ventures into new territory to circumvent Congress and redirect military funding for other purposes, drawing condemnation and confusion from lawmakers across both political parties.
In a conference call with reporters before the announcement, senior administration officials detailed the specifics of the plan. In addition to the $1.4 billion for wall construction appropriated by Congress , approximately $6 billion will be taken from Title X funding and $600 million will be tapped from the Treasury forfeiture fund.
A senior administration official said the wall construction would follow the same design as the one appropriated by Congress, using a steel bollard wall instead of concrete or other prototype walls.
"There's not a fight over what's going to be built," an official said.
White House Acting Chief of Staff Mick Mulvaney also downplayed the assertion that what Trump is doing is in any way unprecedented.
"There's been some concern in the media about whether or not this creates a dangerous precedent," Mulvaney told reporters. "It actually creates zero precedent. This is authority given to the president in the law already. It's not as if he just didn't get what he wanted so he's waving a magic wand and taking a bunch of money."
"I saw Nancy Pelosi said yesterday this sets a precedent for the Democrats to declare a gun emergency the next time they're in the Oval Office. That's completely false," he added. "If Democrats could've figured out a way to do it, they would have done that already."
Trumps decision confounded Republicans worried about an overreaching executive
Rep. Mac Thornberry of Texas, the ranking Republican on the House Armed Services Committee, said in a statement he urged Trump "not to divert significant Department of Defense funding for border security."
"Doing so would have detrimental consequences for our troops as military infrastructure was one of the accounts most deprived during the Obama-era defense cuts," Thornberry said. "And it would undercut one of the most significant accomplishments of the last two years beginning to repair and rebuild our military. I hope that the President will pursue other options."
On the other hand, Republicans loyal to the president, like House Minority Leader Kevin McCarthy, praised Trump for taking swift action.
"We face a humanitarian andnationalsecurity crisis at the border that must be addressed and the Presidents declaration is merely a statement of fact," he said in a statement. "With the declaration and other legal authorities, the President has access to important tools to take the steps necessary to secure the border."
Legal challenges are almost certain
Long before Trump made the decision but was hanging it over Congress' head during the government shutdown, Republicans questioned the legality of an emergency declaration, including supporters of the move like South Carolina Sen. Lindsey Graham.
Democrats have vowed to fight it in every way they can and are confident the White House will be rebuked by the courts.
"A declaration of national emergency would be absolutely repugnant and abhorrent to our constitutional principles," Democratic Sen. Richard Blumenthal on Connecticut told INSIDER in January. "It would lack any basis in fact or the law and would be struck down by the courts."
And the Department of Justice has already warned the White House that the courts will likely block the emergency declaration at least temporarily, ABC News reported .
SEE ALSO: Heres what you need to know about the border security compromise that could avert another government shutdown
