With the Democratic-controlled House’s approval of the same resolution last month, Senate passage sends it to Trump. He has shown no reluctance to casting his first veto to advance his campaign exhortation to “Build the Wall,” and it seems certain Congress will lack the two-thirds majorities that would be needed to override him.

“I’ll do a veto. It’s not going to be overturned,” Trump told reporters in the Oval Office. “It’s a border security vote.”

Though Trump seems sure to prevail in a veto battle, it remains noteworthy that lawmakers of both major political parties resisted him in a fight directly tied to his cherished campaign theme of erecting a border wall.

The roll-call came just a day after the Senate took a step toward a veto fight with Trump on another issue, voting to end US support for the Saudi Arabian-led coalition’s war in Yemen.

In a measure of how remarkable the confrontation was, Thursday was the first time Congress has voted to block a presidential emergency declaration since the National Emergency Act became law in 1976.

Even before Thursday’s vote, there were warnings that Republican senators resisting Trump could face political consequences. A White House official said Trump would not forget when senators who oppose him want him to attend fundraisers or provide other campaign help. The official spoke on condition of anonymity because of a lack of authority to speak publicly on internal deliberations.

US House strikes down Trump’s national emergency

At the White House, Trump did not answer when reporters asked if there would be consequences for Republicans who voted against him.

Underscoring the political pressures, Republican Senator Thom Tillis of North Carolina, who last month became one of the first Republicans to say he’d oppose Trump’s border emergency, reversed himself on Thursday and said he’d vote to support it.

Tillis, who faces a potentially difficult re-election race next year, cited talks with the White House that suggest Trump could be open to restricting presidential emergency powers in the future.

Still, the breadth of opposition among Republicans suggested how concern about his declaration had spread to all corners of the party.

Republican senators voting for the resolution to block Trump included Mitt Romney of Utah, the party’s 2012 presidential candidate; Mike Lee, also of Utah and a solid conservative; Maine moderate Susan Collins and Lamar Alexander of Tennessee, a respected centrist.

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Republicans control the Senate 53-47. Democrats solidly opposed Trump’s declaration.

Presidents have declared 58 national emergencies since the 1976 law, but this was the first declaration aimed at gaining access to money that Congress had explicitly denied, according to Elizabeth Goitein, co-director for national security at New York University Law School’s Brennan Centre for Justice.

Trump and Republicans backing him said a legitimate security and humanitarian crisis exists at the border with Mexico. They also said that Trump was merely exercising his powers under the law, which largely leaves it to presidents to decide what a national emergency is.

“The president is operating within existing law, and the crisis on our border is all too real,” said Senate Majority Leader Mitch McConnell, Republican of Kentucky.

Opponents said that Trump’s assertion of an emergency was overblown. They said he issued his declaration only because Congress agreed to provide less than US$1.4 billion for barriers and he was desperate to fulfil a campaign promise to build the wall.

They noted that the Constitution gives Congress, not presidents, control over spending and said that Trump’s stretching of emergency powers would invite future presidents to do the same for their own concerns.

“He’s obsessed with showing strength, and he couldn’t just abandon his pursuit of the border wall, so he had to trample on the Constitution to continue his fight,” said Senate Minority Leader Chuck Schumer, a New York Democrat.

Republicans had hoped that Trump would endorse a separate bill by Lee. It would have constrained future emergency declarations and was thought likely to win over enough Republican senators to reject Thursday’s resolution.

But Trump told Lee on Wednesday that he opposed the alternative legislation, prompting Lee himself to say he would back the Thursday resolution.

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Should he veto the resolution, the strongest chance of blocking Trump remains several lawsuits filed by Democratic state attorneys general, environmental groups and others.

On Twitter, Trump called on Republicans to oppose the resolution, which House speaker Nancy Pelosi, a California Democrat, helped pass through the House of Representatives last month.

“Today’s issue is BORDER SECURITY and Crime!!! Don’t vote with Pelosi!” Trump tweeted.

Republican Senator Lindsey Graham, who is backing Trump, went to the White House late on Wednesday with other senators to see if some compromise could be reached that would help reduce the number of Republican senators opposing Trump, according to a person familiar with the visit who described it on condition of anonymity. The effort fell short.

The National Emergency Act gives presidents wide leeway in declaring an emergency. Congress can vote to block a declaration, but the two-thirds majorities required to overcome presidential vetos make it hard for legislators to prevail.

Lee had proposed letting a presidential emergency declaration last 30 days unless Congress voted to extend it. That would have applied to future emergencies but not Trump’s current order unless he sought to renew it next year.