This article is more than 1 year old

This article is more than 1 year old

Democrats are moving quickly to try to roll back Donald Trump’s declaration of a national emergency to siphon billions of dollars from the military to fund construction of a fence along the US-Mexico border.

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The Democratic-controlled House is set to vote on Tuesday afternoon on legislation to revoke Trump’s executive order from earlier this month. It is expected to pass, sending it to the Republican-held Senate, where it would take only a handful of GOP defections to pass it.

Trump could use his first-ever veto to kill the measure if it passes Congress, but the White House is seeking to minimize defections among the president’s Republican allies to avoid embarrassment.

The vote could be challenging for Republican lawmakers who view themselves as conservative protectors of the constitution and the powers of the federal purse that are reserved for Congress. But Republican vote counters are confident that the tally will not get near the two-thirds that would overturn a Trump veto.

Democratic leaders said on Monday that the vote is not about the merits of Trump’s wall but how Trump is trampling on the constitution by grabbing money that he cannot obtain through normal means.

“The beauty of the constitution, the heart and soul of the constitution, is the separation of power – co-equal branches of government to be a balance of power,” said the House speaker, Nancy Pelosi.

“The constitution spells out the responsibilities, giving the Congress of the United States, among other powers, the power of the purse. The president’s power grab usurped that constitutional responsibility and fundamentally violates the balance of power envisioned by our founders.”

The minority leader, Kevin McCarthy, said GOP defections would be kept well below the threshold required to sustain a veto. Describing the argument GOP leaders are using to tamp down Republican opposition, he said, “There’s an emergency along the border.”

“If Republicans vote their beliefs, we’ll get a lot. If they vote their party, we won’t get a lot,” said the majority leader, Steny Hoyer.

Trump tweeted on Monday to urge Senate Republicans to stick with him.

“I hope our great Republican senators don’t get led down the path of weak and ineffective border security,” Trump wrote. “Without strong borders, we don’t have a country – and the voters are on board with us. Be strong and smart, don’t fall into the Democrats’ ‘trap’ of open borders and crime!”

Mike Pence is expected to discuss the issue with Republican senators during their weekly private lunch on Tuesday. A justice department official is also expected to attend.

On Monday, the Republican senator Thom Tillis said he would vote to block the order, joining Maine’s Susan Collins and Alaska’s Lisa Murkowski as Republicans supporting the resolution. Congress must defend its power of the purse and warned that a future Democratic president might abuse the power to advance “radical policies”, Tillis said.

At issue is Trump’s longstanding vow to build a wall along the 1,900-mile south-west border, perhaps his top campaign promise. He has long since dropped any pretense that money for the wall would come from Mexico, which he once claimed would be the source of funding.

Earlier this month Congress approved a huge spending bill providing nearly $1.4 billion to build 55 miles (89km) of border barriers in Texas’s Rio Grande Valley, ending a dispute that had led to a record 35-day partial shutdown of the government. Trump had demanded $5.7bn to construct more than 200 miles (322km).

On Monday, national security experts and former GOP lawmakers issued public declarations against Trump’s edict, saying that the situation along the southern border is not a genuine emergency and that Trump is abusing his powers.

“We are aware of no emergency that remotely justifies such a step,” wrote 58 former senior national security officials, including Republican Chuck Hagel, a former Nebraska senator and defense secretary.

In addition, 28 Republican former House members and senators, many of them from the party’s shrinking moderate wing, wrote an open letter declaring their opposition to Trump’s emergency declaration.