Senators unveiled a resolution on Thursday to block President TrumpDonald John TrumpTrump mocks wind power: 'When the wind doesn't blow, just turn off the television' Pentagon investigator probing whether acting chief boosted former employer Boeing Trump blasts McCain, bemoans not getting 'thank you' for funeral MORE's emergency declaration to construct the U.S.-Mexico border wall.

Sens. Tom UdallThomas (Tom) Stewart UdallOvernight Energy: DC moves closer to climate lawsuit against Exxon | Dems call for ethics investigation into Interior officials | Inslee doubles down on climate in 2020 bid Dem lawmakers call for investigation into Interior officials over alleged ethics violations The Hill's 12:30 Report: Manafort sentenced to total of 7.5 years in prison MORE (D-N.M.) and Susan CollinsSusan Margaret CollinsSenate GOP poised to go 'nuclear' on Trump picks Overnight Health Care: CDC pushes for expanding HIV testing, treatment | Dem group launches ads attacking Trump on Medicare, Medicaid cuts | Hospitals, insurers spar over surprise bills | O'Rourke under pressure from left on Medicare for all Dem group launches ads attacking Trump's 'hypocrisy on Medicare and Medicaid cuts' 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 MurkowskiRed dresses displayed around American Indian museum to memorialize missing, murdered native women Juan Williams: Don't rule out impeaching Trump The 25 Republicans who defied Trump on emergency declaration MORE (R-Alaska) and Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenSenate Dems petition Saudi king to release dissidents, US citizen Senators offer bipartisan bill to fix 'retail glitch' in GOP tax law Overnight Energy: EPA moves to raise ethanol levels in gasoline | Dems look to counter White House climate council | Zinke cleared of allegations tied to special election 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 TillisOvernight Health Care: CDC pushes for expanding HIV testing, treatment | Dem group launches ads attacking Trump on Medicare, Medicaid cuts | Hospitals, insurers spar over surprise bills | O'Rourke under pressure from left on Medicare for all Dem group launches ads attacking Trump's 'hypocrisy on Medicare and Medicaid cuts' Trump keeps tight grip on GOP MORE (N.C.).

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