President Donald Trump declared a state of emergency Friday to free up $8 billion in funding to build his long-promised border wall along the U.S.-Mexico border.

Trump is also expected to sign a federal spending bill, which passed the House and Senate on Thursday after three weeks of negotiations, and avoid another government shutdown over border security. The language of the compromise, notably absent the word “wall,” includes just $1.37 billion in funding, far short of the $5.7 billion Trump had demanded from Democrats.

“I’m going to be signing a national emergency, and it’s been signed many times before. It’s been signed by other presidents,” Trump said. "We're talking about an invasion of our country, with drugs, with human traffickers, with all types of gangs." The move is sure to ignite a legal battle that would test the constitutional norms around presidential power. "There would be lawsuits immediately,” Elizabeth Goitein, co-director of the Brennan Center for Justice's Liberty and National Security Program, told VICE News in January. _(Read more about the likely legal battle over Trump's national emergency declaration.**)_**

With his emergency declaration, Trump plans to "unlock" a total of $8 billion in funding, including the $1.37 billion from Congress, to build 234 miles of wall, acting White House chief of staff Mick Mulvaney told reporters Friday morning. That includes:

$600 million from a Treasury Department forfeiture fund

$2.5 billion from a Department of Defense counter-drug activities fund

$3.6 billion in military construction money

“We assess that with the $8 billion, we should have sufficient money this year to do what we wanted to do with the $5.7 billion worth of money that the president asked for originally,” Mulvaney said.

The president failed to pressure Democrats into allocating $5.7 billion for the wall by igniting the longest government shutdown in U.S. history, during which he repeatedly threatened to bypass Congress and use his powers of emergency. It’s a last-ditch attempt to construct the “physical barrier,” which could cost American taxpayers as much as $70 billion, by some estimates.

During his announcement in the Rose Garden Friday, Trump accused Democrats of lying when they cite that most illegal drugs enter the U.S. through legal ports of entry. (Ninety percent of drugs do.) He also rambled off-the-cuff about border security at length and said that human trafficking happens outside of legal ports of entry because border guards would notice “three women with tape on their mouth.”

It’s fairly common for presidents to declare states of emergency. Right now, there are more than 30 active national emergencies. In November, for example, Trump issued an executive order to declare a national emergency — ”a threat to national security” — to impose sanctions against people the U.S. government said were responsible for human-rights abuses in Nicaragua.

Still, issuing a national emergency to get money to complete a partisan campaign promise, one Trump has repeatedly insisted Mexico would foot the bill for, is a different story. The move triggered outrage from Democratic leaders, who said Trump is setting an alarming precedent for future presidents to overreach with executive power.

"A Democratic president can declare emergencies, as well," House Speaker Nancy Pelosi said Thursday. "So the precedent that the president is setting here is something that should be met with great unease and dismay by the Republicans."

Rep. Alexandria Ocasio Cortez, a Democrat from New York, said on Instagram Friday that she and Rep. Joaquin Castro of Texas would introduce legislation to block Trump’s national emergency declaration.

Numerous Republicans also voiced concern over the president’s decision to declare an emergency to get money to build a wall.

"I think it's a mistake," said Sen. Susan Collins, Republican of Maine. "The National Emergencies Act was contemplated to apply to natural disasters or catastrophic events such as the attacks on our country on 9/11. For the President to use it to re-purpose billions of dollars, that Congress has appropriated for other purposes that has previously signed into law, strikes me as undermining the appropriations process, the will of Congress, and being of dubious constitutionality."