WASHINGTON (AP) — House Speaker Nancy Pelosi is trying to make it harder for Republicans to avoid an embarrassing Senate rebuff of President Donald Trump's effort to steer billions of extra federal dollars to building barriers along the U.S.-Mexico border by declaring a national emergency.

As the White House and GOP senators sought a compromise on curbing a president's power to unilaterally declare such emergencies in the future, Pelosi said Wednesday that the House would not take up that legislation if it passed the Senate.

GOP senators are hoping that if Trump endorses that bill, more Republicans would oppose a separate resolution, set for a vote Thursday, that would block the border emergency he proclaimed last month.

If Trump's border emergency stands, he could divert $3.6 billion from military construction projects to build border barriers, even though Congress had voted to limit him to less than $1.4 billion for such construction.

Pelosi's move seemed aimed at persuading GOP senators wavering over the resolution disapproving Trump's border emergency that they would get no political protection by supporting the bill curbing future emergencies because it will never become law.

"Republican Senators are proposing new legislation to allow the President to violate the Constitution just this once in order to give themselves cover," Pelosi, D-Calif., said in a statement. "The House will not take up this legislation to give President Trump a pass."

It has long looked like the Republican-run Senate would join the Democratic-led House in voting to block Trump's border emergency. That would set up the first veto of Trump's presidency.

But there have been signs that opposition by a few GOP mavericks is softening. Some Republicans think Trump went too far in declaring an emergency, but they also are eager to avoid defying a president popular with conservative voters.

An administration official said Wednesday that the White House is skeptical there will be enough votes to head off a Senate defeat Thursday and is reluctant to back limits on future declarations unless a victory on the resolution is assured. The official was not authorized to publicly private conversations and spoke on condition of anonymity.

GOP Sens. Mike Lee of Utah and Thom Tillis of North Carolina and others are trying to work out a compromise with the White House over future emergencies. They also were among five GOP senators who met privately Tuesday at the Capitol with Vice President Mike Pence as Republicans tried to find a way to bolster support for Trump.

Tillis and three other GOP senators have said they would vote with Democrats to support the resolution blocking Trump's border emergency — enough to assure its passage, assuming all Democrats vote "yes" as expected.

At a closed-door lunch Tuesday, Tillis suggested he could be open to backing the president, said two people familiar with his comments. One said Tillis told his colleagues he could change his vote if Trump was indeed ready to curb presidential powers to declare emergencies without Congress' approval.

The two spoke on condition of anonymity to reveal private conversations. A Tillis aide did not return messages left for him. Tillis faces a potentially tough re-election fight next year.

Republicans control the Senate 53-47, meaning that four GOP defections would be enough to send the resolution blocking Trump's border emergency to the White House. The others are Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Rand Paul of Kentucky.

Paul said earlier this month that there were "at least 10" GOP senators prepared to oppose Trump's emergency. But he now expects fewer defections. Still, Congress would be highly unlikely to muster the two-thirds majorities needed to eventually override a veto.

But approval of the resolution would highlight a clash in which Trump was being forced to protect his signature campaign promise by vetoing legislation sent to him by a Republican-led Senate. Congress has never before voted to overturn a president's emergency declaration.

Under a 1976 law, presidents have wide discretion in determining when a national emergency has occurred. Congress can vote to block an emergency declaration, but the two-thirds majorities required to overcome presidential vetoes make it hard for lawmakers to prevail.

Lee's proposal says a presidential emergency would last 30 days unless Congress votes to extend it. It would apply to future emergencies, not Trump's current border emergency.

A vote on Lee's plan was expected after Congress returns from a recess later this month.

The strongest chance of blocking Trump's border emergency is likely several lawsuits filed by Democratic state attorneys general, environmental groups and others.

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Associated Press writer Catherine Lucey contributed to this report.