President Donald Trump will declare a national emergency to bypass Congress and build his long-promised wall along the nation’s southwestern border even as he agreed to sign a spending package that does not finance it, the White House said on Thursday local time.

The announcement came just minutes before the Senate voted 83-16 to advance the spending package in anticipation of final passage Thursday night by the House, in effect ending a two-month war of attrition that closed much of the federal government for 35 days and threatened a second shutdown on Saturday (Friday local time).

But if he declares a national emergency to access billions of dollars for his wall, Mr Trump could instigate a constitutional clash over who controls the federal purse and test the bounds of presidential authority in a time of divided government.

Democrats and some Republicans instantly condemned the move, with some vowing to challenge it through legislation and lawsuits.

“President Trump will sign the government funding bill, and as he has stated before, he will also take other executive action — including a national emergency — to ensure we stop the national security and humanitarian crisis at the border,” said Sarah Huckabee Sanders, the White House press secretary.

“The president is once again delivering on his promise to build the wall, protect the border and secure our great country.”

Mr Trump’s announcement capped hours of last-minute drama as he came under pressure on Friday (Thursday morning local time) to not sign the spending legislation from conservative figures like Laura Ingraham, who denounced it on Twitter as a “monstrosity” and a “Total SCAM!”

This 1,169 page monstrosity will green light more “family units” crossing illegally—without a doubt.

— Laura Ingraham (@IngrahamAngle) February 14, 2019

A balky president considered telling Republican leaders to put aside the measure, brokered by both parties, and instead pass a short-term bill to keep the government open while allowing him to resume efforts to win border wall money, according to a Republican briefed on the situation.

Such a move would have unravelled the delicate bipartisan balance favoured by Republican Senator Mitch McConnell, the majority leader, who wanted to move beyond the wall fight.

In a telephone conversation on Friday (Thursday local time), Mr Trump asked Senator McConnell whether the spending measure included any hidden provisions or “land mines,” and the senator reassured him it did not, according to a person familiar with the call.

The White House says Mr Trump is taking the emergency action to ensure the crisis on the border is stopped. Photo: Samuel Corum/The New York Times

Ultimately, Mr Trump was persuaded to sign the bipartisan spending measure after all, and at least some close to the president doubted that he was ever really wavering and instead was just enjoying the suspense.

But Senator McConnell chose not to take a chance, rushing to the floor and interrupting a colleague’s speech to announce Mr Trump’s decision, in effect locking it in before he could change his mind.

In agreeing to end the spending fight for now, however, Mr Trump essentially started a new one with his vow to declare a national emergency, one that crosses party and ideological lines as liberals and conservatives alike objected to what they called presidential overreach.

Seven senate Democrats, including four announced or possible presidential candidates, immediately introduced legislation intended to block Mr Trump from diverting money from disaster relief for the wall.

Some House Democrats, including Republican Jerrold Nadler of New York, chairman of the Judiciary Committee, began endorsing a joint resolution to essentially nullify a national emergency declaration.

House Speaker Nancy Pelosi. Photo: Sarah Silbiger/The New York Times

A parade of liberal advocacy organisations sent out pre-written statements promising to challenge any such declaration in court as “an outrageous abuse of power” by an “unstable and increasingly autocratic” president, as one of the groups, Public Citizen, put it.

“The president is doing an end run around Congress,” House Speaker Nancy Pelosi of California told reporters.

She suggested that Mr Trump was setting a precedent for future Democratic presidents to act on issues like gun control – precisely the scenario that scares Republicans.

“You want to talk about a national emergency, let’s talk about today,” Ms Pelosi said, reminding Trump that it was the anniversary of the shooting massacre last February at Marjory Stoneman Douglas High School in Parkland, Florida.

Seventeen students and staff members were killed.

That’s a national emergency. Why don’t you declare that emergency, Mr. President? I wish you would.”

Democratic leader Senator Chuck Schumer of New York echoed her criticism and said Congress would defend its prerogatives.

“The public was more opposed to the emergency declaration than they were to the wall,” he said in a brief interview. “And they were opposed to the wall.”

About a half-dozen Senate Republicans quickly spoke out against the move, as well.

“I don’t think this is a matter that should be declared a national emergency,” said Senator Lisa Murkowski of Alaska.

“We as legislators are trying to address the president’s priority. What we’re voting on now is perhaps an imperfect solution, but it’s one we could get consensus on.”

We’ve just passed a bill that will keep the government open and finalize our remaining appropriations bills for FY 2019. This funding package addresses some of our border security issues, fully funds a heavy polar security cutter, as well as a range of other initiatives. pic.twitter.com/lZ9Dyxt6Ys

— Sen. Lisa Murkowski (@lisamurkowski) February 15, 2019

Among the Republicans who privately warned Mr Trump against an emergency declaration was Senator McConnell, who expects that House Democrats will pass a non-binding resolution disapproving it in a form that the Republican leader cannot block from a floor vote.

At least five or six Republican senators are likely to vote against the president, making a majority along with the Democrats.

A person familiar with the discussions said that Senator McConnell said that he has warned Mr Trump that he has less than two weeks to try to persuade wavering Republicans to support his national emergency effort, otherwise he will face the prospect of a bipartisan rebuke by Congress.

The spending legislation headed to passage on Friday (Thursday local time) includes the seven remaining bills to keep the remainder of the government open through the rest of the fiscal year at the end of September.

House and Senate negotiators unveiled the 1159-page bill on Thursday (Wednesday local time) just before midnight, leaving little time for lawmakers to actually digest its contents.

The border security compromise tucked into the bill is perhaps the most stinging legislative defeat of Trump’s presidency.

It provides $US1.375 billion ($1.9 billion) for 88.5 kilometres of steel-post fencing, essentially the same deal that Mr Trump rejected in December, triggering the shutdown, and far from the $US5.7 billion ($8 billion) he demanded for more than 321.8km of steel or concrete wall.

The measure prohibits construction in certain areas along the Rio Grande Valley and includes a provision, pushed by Republican Henry Cuellar, granting communities on the border time to weigh in on the location and design of the fencing.

The bill also prohibits funds from being used to keep lawmakers from visiting and inspecting Department of Homeland Security detention centres, following a number of highly publicised instances where Democratic lawmakers tried to visit detention centres and were turned away.

Mr Trump’s aides have told him he can add to the $US1.375 billion ($1.9 billion) by reallocating money from other related programs using his traditional discretion but a national emergency would allow him to access even more money.

Exactly how that would work was still being debated; there were multiple drafts of the emergency order circulating within the government this week.

A Defence Department official said one likely scenario would be to divert up to $US2.5 billion ($3.5 billion) in counternarcotics funds to the Army Corps of Engineers.

The administration would then transfer existing federal land along the border to the Defence Department and acquire or condemn private land.

The Army Corps could then go ahead and build a wall or other barrier to secure the Defence Department’s property using the newly diverted funds.

Dozens of miles of barrier could be built this way, according to the official, who asked not to be identified discussing alternatives before the White House was ready to disclose a specific plan.

-New York Times