The US House of Representatives was poised to vote to terminate President Donald Trump’s proclaimed national emergency at the US-Mexico border. Picture: Reuters

Washington - The US House of Representatives was poised on Tuesday to vote to terminate President Donald Trump’s proclaimed national emergency at the US-Mexico border, in what would be another stinging rejection of his proposed border wall.

If the Democratic-controlled House approves a resolution ending the president's emergency, as expected, the measure would go to the Republican-controlled Senate where its chances of passage were slimmer but seemed to be improving.

Senator John Barrasso, a member of the Senate's leadership, told MSNBC in an interview that the legislation "may actually pass the Senate."

Meanwhile, the White House formally notified Congress, as expected, that if the measure passes Congress, Trump's advisers would recommend that he veto it in order to maintain the power he activated on February 15 as a way of circumventing Congress.

Trump argues he has the power to proclaim a national emergency to unilaterally direct existing money for building a border wall that Congress has refused to fully fund.

"The current situation at the southern border presents a humanitarian and security crisis that threatens core national security interests and constitutes a national emergency," the White House statement warned.

A Trump veto would be the first of his presidency and the first since Republicans lost majority control of the House in last November's elections.

Overriding such a veto in Congress would require two-thirds majorities in both chambers, making it highly unlikely, said lawmakers.

"When you see the vote today, there will be nowhere near the votes to override a veto," US Representative Steve Scalise, the No. 2 House Republican, told reporters on Capitol Hill on Tuesday.

The battle in Congress is the latest chapter in a long-running war between Trump and Democrats over border security, immigration policy and the "great, great wall" that Trump has pledged to build since becoming a presidential candidate.

He originally promised that Mexico would pay for it, but after Mexico refused, he asked US taxpayers to foot the bill for a project Democrats say is unneeded and will not be effective.

In his first two years in office, Trump's Republicans controlled both chambers of Congress, which under the US Constitution holds the national purse strings, but lawmakers failed to provide the funding Trump wanted for his border barrier.

When Congress, with the House now controlled by Democrats, refused in recent weeks to provide the money he wants, Trump declared an emergency and vowed to divert funds toward the wall from accounts already committed by Congress for other purposes.

That set up a test of the constitutional separation of powers between Congress and the presidency that will likely lead to a court challenge after lawmakers deal with the resolution.

A coalition of 16 US states led by California has already sued Trump and top members of his administration to block his emergency declaration.

Writing on Twitter on Monday, Trump, who says the wall is needed to stop illegal immigration and drugs, warned Republicans not to "fall into the Democrats 'trap' of Open Borders and Crime!"

Republican Representative Justin Amash is co-sponsoring the resolution in the House, along with more than 230 House Democrats, and Amash is urging his colleagues to support it.

"The same congressional Republicans who joined me in blasting Pres. Obama’s executive overreach now cry out for a king to usurp legislative powers," Amash wrote on Twitter.

The White House was working to limit Republican support for the measure, especially in the Senate. Vice President Mike Pence was scheduled to attend a Senate Republican luncheon on Tuesday, where the resolution was expected to be a key topic.

Republican Senator Thom Tillis, in an opinion article published in the Washington Post, said he backed Trump on border security, but would vote for the resolution because he "cannot justify providing the executive with more ways to bypass Congress."

At least two other Republican senators, Susan Collins and Lisa Murkowski, have said they will likely support the measure, too. For it to pass the Senate, at least one more Republican vote would be needed, assuming all Democrats and two independents back it.

Trump declared the emergency after Congress declined his request for $5.7 billion to help build the wall. Instead, Congress this month appropriated $1.37 billion for building border barriers.

Reuters