WASHINGTON – President Donald Trump declared a national emergency Friday to free up billions of dollars for a border wall, a highly controversial move that Democrats and some Republicans have criticized as an overreach of his power.

The announcement, made in the White House Rose Garden, came as Trump was preparing to sign a bill that prevents another government shutdown and also provides $1.375 billion for border fencing – far less than the $5.7 billion the president had demanded for a wall along the U.S.-Mexico border.

"We’re going to confront the national security crisis on our southern border, and we’re going to do it one way or another," Trump said, speaking to an audience that included border patrol agents and "Angel Moms," who are parents of children killed by immigrants in the country illegally.

The emergency declaration is expected to create an extended legal and political battle. Trump himself predicted the issue would end up before the Supreme Court.

"I expect to be sued," he said. But, "we’ll win, I think.”

As Trump was speaking, Senate Minority Leader Chuck Schumer, D-N.Y., and House Speaker Nancy Pelosi, D-Calif., issued a joint statement accusing the president of going "outside the bounds of the law" to try to achieve what he failed to persuade Congress to do.

"The Congress will defend our constitutional authorities in the Congress, in the courts, and in the public, using every remedy available," they said.

Democrats have talked about taking up a resolution in Congress to thwart Trump's action – although their measure would likely face a presidential veto.

White House aides said Trump is expecting to have $8 billion in total for the wall, including the money Congress approved as well as funds he is tapping from the Pentagon and other sources. Some of that money he can access only through the use of the national emergency.

Trump said his push for a wall is "not complicated."

"It's very simple: We want to stop drugs from coming into our country, we want to stop gangs from coming into our country," he said.

But an analysis of data from the southern border indicates that the vast majority of narcotics enters through U.S. ports of entry, not the wide swaths of border in between where additional barriers could be erected, experts say.

Legal challenges to the emergency declaration could delay construction of Trump's proposed border wall, but the battle would give Trump a potent political issue to run on in the 2020 presidential election.

Critics said the president’s own remarks appeared to undermine the urgency on the border, where migrant crossings are far lower than they were a decade ago.

“I didn't need to do this: I just wanted to (build the wall) much faster,” Trump said. “The only reason we're up here talking about this is because of the election."

Some Republicans, including Sen. Marco Rubio, R-Fla., have warned that Trump could be violating the Constitution and setting a bad precedent.

"We have a crisis at our southern border, but no crisis justifies violating the Constitution," Rubio said.

Trump said he doesn't want to stop with just a wall – he also would like to see major immigration reform. "We have real problems," he said.

More:Trump's emergency declaration would trigger a drawn out legal fight

Trump's declaration of a national emergency came just hours after Congress approved legislation to keep the government funded past midnight Friday, when existing funding will lapse. Trump signed it after his Rose Garden news conference.

The measure was pieced together by a bipartisan group of budget negotiators from the House and the Senate. It would, among other things, spend $1.375 billion for a barrier along the Texas border and require the structure be made of previously deployed designs – essentially ruling out concrete but allowing the barrier to made of steel slats.

Trump’s demand for a border wall – a signature promise of his presidential campaign – was at the center of a budget standoff that triggered a record 35-day government shutdown late last year. The shutdown ended in late January when lawmakers passed a temporary funding bill to buy them time to work out an agreement on border security.

Contributing: Eliza Collins, Christal Hayes, Deborah Berry, Ledyard King, Maureen Groppe

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