Washington - y Shabtai Gold - US President Donald Trump declared the situation at the border with Mexico a national emergency on Friday, in a move that enables him access to money to build hundreds of kilometres of physical barriers on the southern frontier.
The decision has been roundly criticized by Democrats, who say there is no national emergency and Trump is attempting a power grab. It will likely be contested in Congress and in the courts.
In a statement outside the White House, Trump conceded he may lose some of the initial legal challenges, but justified his decision.
"We are talking about an invasion of our country, with drugs and human traffickers and all types of criminals and gangs," Trump said in the Rose Garden.
Trump said the wall he wanted could be built more slowly, if he went through normal legislative channels.
"I can do a wall over a longer period of time, I don't need to do this, but I'd rather do it much faster," he said. His phrasing set off an immediate debate about why he is declaring an emergency if the move is not needed.
Trump will use 8 billion dollars for the wall, of which 1.375 billion was appropriated by Congress for barriers, far below the president's demand of 5.7 billion to build some 377 kilometres of wall.
The rest will come from executive action and the national emergency declaration, split about evenly, by taking money from the Pentagon's construction budget and drug forfeitures. It is unclear how the White House will pay the military back.
Opponents have rejected Trump's description of the situation at the border as a national security threat, saying illegal immigration is down from its peaks and the majority of drugs come through ports of entry and not by smugglers crossing the frontier in areas without walls.
Democrats have accused Trump of "a gross abuse of the power," a "power grab" and "naked contempt for the rule of law."
Trump has been defiant, saying repeatedly "walls work 100 per cent," while insisting he was not focused on the wall solely because it was a campaign promise, a jab often employed by critics.
"What we really want to do is simple, it's not like its complicated, it's very simple: We want to stop drugs coming into our country, we want to stop criminals and gangs coming into our country," Trump said in his address during a sunny day at the Rose Garden.
Some members of Trump's own Republican party have expressed concerns about the national emergency, fearing both a degradation of the role of Congress and that it will set a precedent.
The White House has tried to point out that national emergencies have been used before, even to move around money, although those cases were of far smaller amounts and came during the first Gulf War and after the September 11, 2001, terrorist attacks.
"It's not as if he didn't get what he wanted and waved a magic wand to get some money," one official said about the president.
Democrats in the House of Representatives say they will draft a bill to challenge Trump. If it also passes in the Senate, Trump could be forced to wield a veto.
"The Congress cannot let the president shred the constitution," leading Democrats Speaker Nancy Pelosi and Senator Chuck Schumer said.
Trump pushed the federal government into the longest shutdown in history, ending last month after 35 days. His own party was against another shutdown.
Trump announced his intention to declare the emergency a day before funding for the government was again set to run out and as Congress was approving appropriations, but without cash for Trump's wall.
The president, who is set to spend the upcoming weekend at his resort in Florida, has agreed to sign the funding bill and keep government open.
The entire process on the border is being denounced by Democrats as a blatant attempt to bypass Congress, which is constitutionally viewed as holding the federal purse strings.
Trump campaigned on the border wall and pledged Mexico would pay for it, something that has not materialized.