President Donald Trump announced Friday that he will declare a national emergency in order to build a wall on the US – Mexico border without funding from Congress , a rare step immediately slammed by Democrats as an unlawful “ power grab . ”

The extraordinary declaration frees Trump to seek to redirect billions of dollars of federal funds to stop what he called an “ invasion ” of drugs , gangs , human traffickers and undocumented migrants across the southern US border .

“ I ’ m going to be signing a national emergency … Everyone knows that walls work, ” the president told reporters at the White House.

Trump made the declaration after agreeing to a spending measure that will keep federal agencies operational through September 30 — a relief for lawmakers who had fretted about the possibility of a second crippling government shutdown .

But the measure falls wells short of the $ 5 . 7 billion that Trump has been demanding for a wall on the 2 , 000 -mile ( 3 , 200 – kilometer) southern border, and the emergency declaration would help him bypass Congress and get the money that lawmakers refused to give him .

“ What we really want to do is simple… We want to stop drugs from coming into our country. We want to stop criminals and gangs from coming into our country, ” Trump said .

The emergency declaration enables the activation of any of hundreds of dormant powers , which can permit the White House to declare martial law , suspend civil liberties , expand the military, seize property and restrict trade, communications and financial transactions .

Article 1 of the US Constitution states Congress gets to decide how money is appropriated and Trump’ s plan to use emergency powers to circumvent congressional opposition to the wall has alarmed US lawmakers , including in his Republican Party , who warn that the move would set a dangerous precedent .

Democrats have signaled that the move would open the door to future presidents declaring emergencies on various topics , from gun violence to climate change to the opioid crisis .

“ The President ’ s unlawful declaration over a crisis that does not exist does great violence to our Constitution and makes America less safe , stealing from urgently needed defense funds for the security of our military and our nation, ” House Speaker Nancy Pelosi and Senate Democratic Leader Chuck Schumer said in a joint statement .

“ This is plainly a power grab by a disappointed President , who has gone outside the bounds of the law to try to get what he failed to achieve in the constitutional legislative process . ”

Members of Pelosi ’ s caucus were “ reviewing our options ” about how to respond to Trump ’ s move , she told reporters Thursday.

Trump said he fully expected his move to be challenged in court — and indeed within minutes the New York state Attorney General Letitia James vowed to “ fight back with every legal tool at our disposal. ”

But the president also voiced confidence that he would prevail in any legal challenge.

“ I expect to be sued , ” he said at the White House. “Sadly it will go through a process and happily, we ’ ll win . I think, ” he said . “ I think that we will be very successful in court . ”