McConnell said he hasn't "reached a total conclusion" about whether Trump's emergency declaration was legal, wouldn't predict whether the GOP-controlled Senate would block an impending resolution aimed at undoing the declaration, and dodged a question about whether he plans to push other GOP senators to vote with Trump during a Tuesday afternoon press conference. Trump has promised a veto and it seems all but certain that Congress won't be able to muster the two-thirds majorities required to override a veto.
But the showdown was forcing Republicans to cast uncomfortable votes pitting their support for a president wildly popular with GOP voters against fears that his expansive use of emergency powers would invite future Democratic presidents to do likewise for their own pet policies.
Castro, chairman of the Congressional Hispanic Caucus, said it will require "historic unity" to pass the bill through Congress, while thanking the bill's 230 co-sponsors in the House of Representatives, up from 220 when it was introduced.
GOP Senator Thom Tillis said in a column that while Trump is "rightfully frustrated with Congress's inaction" on border security, the president made a mistake declaring an emergency and Tillis will support the Democrats' resolution of disapproval.
"I personally couldn't handicap the outcome at this point", said Senate Majority Leader Mitch McConnell, who's planning a vote within the next three weeks.
While passage was a victory for Democratic House Speaker Nancy Pelosi, the tally was short of what she would likely need to override a possible veto by Republican Trump.More news: Johnson clinches 20th title with runaway Mexico win
In a separate letter on Monday, 23 former Republican U.S. lawmakers also urged current members of Congress to pass the resolution, Politico reported.
So far, three - Lisa Murkowski of Alaska, Susan Collins of ME, and Thom Tillis of North Carolina - have already indicated they will vote to block Mr Trump's order. "If the Democrats had been willing to work with us on something more broad and something that would have applied in future situations, I think they would have had a much more bipartisan response to that". Republicans control the chamber, 53-47, but several senators in Trump's party returned to Washington after a one-week break to express deep reservations about Trump's end run around Congress to obtain wall funding.
President Trump is prepared to use his first-ever veto to block the measure if it passes. Richard Lugar, Republican from IN and once the chairman of the Senate's foreign relations committee.
In the Senate, the privileged resolution can sit in committee for up to 15 days before it's available for any member to bring it up for a vote. "Be strong and smart, don't fall into the Democrats "trap" of Open Borders and Crime!"
President Trump's emergency declaration would redirect $3.6 billion in military construction funding; $2.5 billion from the Pentagon's drug interdiction program; and $600 million from the Treasury Department's asset forfeiture fund.
The wall was one of Trump's top campaign promises.
A number of other Republican lawmakers, including Senators Ben Sasse of Nebraska, John Cornyn of Texas, and Marco Rubio of Florida, have cautioned Trump against the national-emergency declaration, but will not support the resolution.