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WASHINGTON — Sen. Mike Lee on Wednesday became the fifth Republican to announce support for the House-passed resolution to terminate President Donald Trump's national emergency declaration to pay for a border well, ensuring the measure will almost certainly pass Thursday.

"For decades, Congress has been giving far too much legislative power to the executive branch," Lee said in a statement.

Lee spoke with Trump Wednesday about the upcoming vote, a senior White House official told NBC News.

Lee had introduced a bill that would end all national emergencies act declarations after 30 days unless Congress affirmatively votes to extend the emergency as a way to get past the impasse, but he acknowledged his legislation wasn't going anywhere at this time.

The measure to terminate Trump's national emergency declaration is expected to be approved by the GOP-controlled Senate because enough Republicans have signaled that they would join Democrats to vote in favor of the measure.

As of last week, at least four Senate Republicans were expected to vote to support the resolution, including Rand Paul of Kentucky, Thom Tillis of North Carolina, Lisa Murkowski of Alaska and Susan Collins of Maine. Senate Leader Mitch McConnell, R-Ky., conceded that the measure would pass.

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Trump, however, is expected to veto the resolution, and it is unlikely to receive enough support in Congress to overturn that veto.

"Republican Senators are overthinking tomorrow’s vote on National Emergency. It is very simply Border Security/No Crime — Should not be thought of any other way," he tweeted. "We have a MAJOR NATIONAL EMERGENCY at our Border and the People of our Country know it very well!"

Meanwhile, Lee introduced his legislation Tuesday, which would amend the 1976 National Emergencies Act to limit the president's power — but it would apply only to future circumstances, not to the current declaration.

His bill would automatically end future emergency declarations after 30 days unless Congress voted to extend the emergency.

"If we don't want our president acting like a king, we need to start taking back the legislative powers that allow him to do so," Lee said.

Speaker Nancy Pelosi said Wednesday, however, that the Democratic-controlled House would not give President Donald Trump and Republicans a way out of the effort to cancel the president's declaration of a national emergency to build his wall.

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

Trump wants to use the emergency declaration to allow him to make an end-run around Congress and get a hold of billions of dollars in existing federal funds so they can be redirected to pay for the construction of a wall or barrier on the U.S. border with Mexico.

Senate Minority Leader Chuck Schumer, D-N.Y., railed against Senate Republicans and their legislation Wednesday.

"Some senators are in search of a fig leaf," Schumer said in remarks on the Senate floor. "They come up with this idea that would change the emergency declaration for future moments. That will not pass."

McConnell said Tuesday that Republicans were discussing ways to amend the National Emergencies Act, but only after they voted on the current resolution.

"There's a lot of discomfort with the law — not that the president doesn't have the authority to do what he is doing," he said. "Is this grant of authority to any president, not just this one, any president — was it too broad back in the ’70s when it was passed?"

In addition to Lee’s proposal, Sen. Ron Johnson, R-Wis., chairman of the Senate Homeland Security Committee, has pitched the idea of passing a nonbinding measure that would simply state the Senate disapproval of any president invoking the law on issues they personally deem to be national emergencies.