Senators unveiled a resolution on Thursday to block President TrumpDonald TrumpSenators given no timeline on removal of National Guard, Capitol fence Democratic fury with GOP explodes in House Georgia secretary of state withholds support for 'reactionary' GOP voting bills MORE's emergency declaration to construct the U.S.-Mexico border wall.

Sens. Tom UdallTom UdallOVERNIGHT ENERGY: Haaland courts moderates during tense confirmation hearing | GOP's Westerman looks to take on Democrats on climate change | White House urges passage of House public lands package Udalls: Haaland criticism motivated 'by something other than her record' Senate approves waiver for Biden's Pentagon nominee MORE (D-N.M.) and Susan CollinsSusan Margaret CollinsKlain on Manchin's objection to Neera Tanden: He 'doesn't answer to us at the White House' Overnight Health Care: Johnson & Johnson vaccine safe, effective in FDA analysis | 3-4 million doses coming next week | White House to send out 25 million masks Biden's picks face peril in 50-50 Senate MORE (R-Maine) introduced the resolution on the Senate floor, where it's expected to be taken up within a matter of weeks.

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The two senators, in back-to-back speeches, stressed that the Senate's vote wasn't about whether a senator supported the U.S.-Mexico border wall or Trump but about maintaining a separation of power between the executive and legislative branches on funding the government.

“I support, strongly support, protecting the institutional prerogatives of the United States Senate and the system of checks and balances that is central to the structure of our government,” Collins said. 

Udall added that the debate over the emergency declaration was about the “strength of the rule of law.”

"This is about protecting the very heart of our American system of government. ... Congress and only Congress holds the power of the purse,” he said.

The Senate resolution, which is also being co-sponsored by Sens. Lisa MurkowskiLisa Ann MurkowskiOvernight Health Care: Johnson & Johnson vaccine safe, effective in FDA analysis | 3-4 million doses coming next week | White House to send out 25 million masks Biden's picks face peril in 50-50 Senate Murkowski undecided on Tanden as nomination in limbo MORE (R-Alaska) and Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenSenators press Treasury to prioritize Tubman redesign Can Palestine matter again? Senate signals broad support for more targeted coronavirus relief checks MORE (D-N.H.), comes two days after the House passed its measure to block Trump’s emergency declaration.

All Democrats are expected to back the resolution once it comes to the Senate floor. They’ll need four Republican senators to get it to Trump’s desk, where he’s said he will veto it.

So far, three Republican senators have said they will vote for the resolution: Collins, Murkowski and Thom TillisThomas (Thom) Roland TillisMcConnell backs Garland for attorney general GOP senators demand probe into Cuomo's handling of nursing home deaths CNN anchor confronts GOP chairman over senator's vote to convict Trump MORE (N.C.).

Several other Republicans have voiced concerns about Trump’s emergency declaration.