President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE on Thursday made a last-ditch effort to stymie the Senate’s expected rebuke of his national emergency declaration at the southwest border, as Republican support for the measure grew.

In a series of morning tweets, Trump renewed his veto threat against a resolution of disapproval senators are scheduled to vote on Thursday afternoon and defended the legality of declaring an emergency to build a border wall without approval from Congress.

The president also floated the possibility of agreeing to changes to the national-emergency law “at a later date,” a proposal floated by Republican senators to avert the standoff, but framed the vote as an ideological litmus test on immigration for the GOP.

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“A vote for today’s resolution by Republican Senators is a vote for Nancy Pelosi Nancy PelosiPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare House lawmakers reach deal to avert shutdown Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE, Crime, and the Open Border Democrats!” Trump tweeted.

Prominent legal scholars agree that our actions to address the National Emergency at the Southern Border and to protect the American people are both CONSTITUTIONAL and EXPRESSLY authorized by Congress.... — Donald J. Trump (@realDonaldTrump) March 14, 2019

....If, at a later date, Congress wants to update the law, I will support those efforts, but today’s issue is BORDER SECURITY and Crime!!! Don’t vote with Pelosi! — Donald J. Trump (@realDonaldTrump) March 14, 2019

The repeated warnings, however, appeared to do little to stem the tide of GOP defections. Sens. Lamar Alexander Andrew (Lamar) Lamar AlexanderGraham: GOP has votes to confirm Trump's Supreme Court nominee before the election The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE (R-Tenn.) and Mitt Romney Willard (Mitt) Mitt RomneySenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-Utah) both announced Thursday morning they would vote for the resolution, joining five other Republican senators who say they will as well.

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Speaking to reporters later at the White House, Trump appeared resigned to the resolution’s passage but expressed confidence it will not be approved with a veto-proof majority.

“I’ll probably have to veto and it’s not going to be overturned,” he said.

Even if the Senate passes the resolution with strong Republican support, it would worsen the sting for Trump, who has made the border wall his signature issue and harangued members of his own party to support his effort to build it. The Democrat-controlled House has already approved the resolution, meaning Trump will be forced to use his veto powers for the first time.

Lawmakers in both parties believe Trump exceeded his authority when he invoked his emergency powers to obtain money for the wall after Congress refused to grant his request for billions of dollars in funding, which had triggered a 35-day government shutdown that dealt a political blow to the GOP.

Despite their constitutional concerns, a number of Republican senators have tried to stave off a direct confrontation with the president that could deepen an intra-party rift on the issue of immigration.

Sens. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (R-Texas), Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) and Ben Sasse Benjamin (Ben) Eric SasseGovernment watchdog recommends creation of White House cyber director position Chamber of Commerce endorses McSally for reelection Ben Sasse is mistaken with idea for the election of senators in America MORE (R-Neb.) reportedly made a surprise visit to the White House on Wednesday night to pitch the president on a compromise plan that could have satisfied the concerns of their colleagues.

But a White House lawyer informed the lawmakers the plan would not work, according to The Washington Post, and Trump forged ahead with his veto threats.

“The legal scholars all say it’s totally constitutional,” Trump said during a meeting with Irish Prime Minister Leo Varadkar. “It’s really a border security vote. It’s pure and simple. It’s a vote for border security. It’s a vote for no crime.”

Trump also suggested that sticking with him on the vote would help the GOP win voters in the 2020 election, even though polls show most voters disapprove of the emergency declaration.

“I think it’s going to be a great election issue,” he said.

Vice President Pence and White House aides have also been working behind the scenes to prevent GOP defections. Pence visited GOP senators on Capitol Hill this week and Trump has spoken by phone with several of them, according to White House officials.

But Trump has only been willing to go so far to address Republicans’ concerns. He personally shot down a proposal floated by Sen. Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (R-Utah) that would have curtailed the president’s emergency powers in exchange for GOP senators’ votes against the resolution.

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Lee announced he would vote for the resolution on Wednesday shortly after hearing from Trump that the plan was a non-starter.

GOP Sens. Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (Ky.), Lisa Murkowski Lisa Ann MurkowskiSenate GOP aims to confirm Trump court pick by Oct. 29: report Senate GOP sees early Supreme Court vote as political booster shot Pence defends Trump's 'obligation' to nominate new Supreme Court justice MORE (Alaska), Susan Collins Susan Margaret CollinsSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (Maine) have also said they will vote for the resolution and Sen. Thom Tillis Thomas (Thom) Roland TillisThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting OVERNIGHT ENERGY: EPA head questions connection of climate change to natural disasters | Pebble Mine executives eye future expansion in recorded conversations | EPA questions science linking widely used pesticide to brain damage in children Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight MORE (R-N.C.) has indicated he will vote in favor of it as well.

The Senate is expected to vote in the afternoon shortly after Trump visits the Capitol with Varadar for the annual “Friends of Ireland” luncheon with members of Congress to mark St. Patrick’s Day.

It comes one day after the Senate voted to end U.S. involvement in the Saudi-led military campaign in Yemen, another break between Trump and the Republican-led Senate that has traditionally supported his policies.