Senators unveiled a resolution on Thursday to block President TrumpDonald John Trump5 things to know about Boris Johnson Conservatives erupt in outrage against budget deal Trump says Omar will help him win Minnesota MORE's emergency declaration to construct the U.S.-Mexico border wall.

Sens. Tom UdallThomas (Tom) Stewart UdallAl Franken says he 'absolutely' regrets resigning Dems open to killing filibuster in next Congress House passes bill to crack down on toxic 'forever chemicals' MORE (D-N.M.) and Susan CollinsSusan Margaret CollinsPoll: McConnell is most unpopular senator Hillicon Valley: Lawmakers struggle to understand Facebook's Libra project | EU hits Amazon with antitrust probe | New cybersecurity concerns over census | Robocall, election security bills head to House floor | Privacy questions over FaceApp Trump angry more Republicans haven't defended his tweets: report 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 MurkowskiPoll: McConnell is most unpopular senator Overnight Defense: Highlights from Defense pick's confirmation hearing | Esper spars with Warren over ethics | Sidesteps questions on Mattis vs. Trump | Trump says he won't sell F-35s to Turkey Epstein charges show Congress must act to protect children from abuse MORE (R-Alaska) and Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenPoll: McConnell is most unpopular senator How to reduce Europe's dependence on Russian energy Epstein charges show Congress must act to protect children from abuse 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 TillisThe Hill's Morning Report — Trump applauds two-year budget deal with 0 billion spending hike Republicans scramble to contain Trump fallout McConnell says Trump is not a racist, but calls for better rhetoric MORE (N.C.).

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