Washington — The Senate failed to advance a national security bill that included sweeping border security reforms on Wednesday, with GOP senators and a handful of Democrats rejecting a deal crafted after months of bipartisan talks.

The bill also included tens of billions of dollars in foreign aid to Ukraine, Israel, Taiwan and other national security priorities. Democratic leaders immediately moved to bring up the foreign aid portions of the legislation on their own, which some Republicans said they would support.

The failure of the immigration deal wipes out four months of negotiations that were originally prompted by Republicans who opposed sending more aid to Ukraine without first tightening the U.S.-Mexico border. A trio of senators released their plan on Sunday, and it contained many of the concessions Republican lawmakers have demanded for years.

But the plan drew fierce criticism from House Republicans and former President Donald Trump, who holds significant sway among GOP lawmakers. All but four GOP senators ended up opposing the border agreement, and the vote to advance it failed 49 to 50. A handful of Democrats also opposed the measure.

Whether the slimmed-down bill can gain the 60 votes needed to move forward in the chamber remains to be seen.

The border security outcome was widely expected, since many Republican senators had said the legislation did not go far enough in stopping border crossings and tightening asylum laws. Senate Majority Leader Chuck Schumer forged ahead with the vote anyway, choosing to put members on the record with their positions.

"Today, senators face a decision several months in the making," Schumer said from the Senate floor ahead of the vote. "Will Senate Republicans vote to start debate — just a debate — on bipartisan legislation to strengthen America's security, stand with Ukraine, and fix our border, or will they cow to Donald Trump's orders to kill this bill?"

The fight over the border and Ukraine

The about-face from Republicans on immigration — opposing border security policies they previously demanded — comes more than four months after the initial standoff over the White House's funding request.

Former House Speaker Kevin McCarthy first touted the move to tie border funds to Ukraine aid in the final days of his speakership last fall, a last-ditch attempt to win over the House conservatives who would eventually vote to oust him. He emphasized at the time that Ukraine wouldn't receive another U.S. aid package "if the border is not secure." And the party quickly coalesced around the idea.

But just four months later, the party largely rejected the border security components of the supplemental, following Trump's lead. Democrats accused GOP lawmakers of refusing to fix the problems at the border since doing so would deprive Trump of one of his central campaign issues.

Two of the negotiators in the border talks, Sen. James Lankford, an Oklahoma Republican, and Kyrsten Sinema, an Arizona independent, defended their agreement on the Senate floor ahead of the votes on Wednesday, appearing exasperated at times by the GOP's swift opposition.

"The bill that's been put together has been a bipartisan effort. Welcome to the United States Senate," Lankford said, noting that neither side got everything they wanted. "You can do a partisan bill in the House, but in the Senate, we have to look at each other across the aisle and then figure out a way to be able to solve this."

Lankford acknowledged that some senators would vote no because of policy differences, which he said were understandable. But he seemed to take issue with those who had "political differences'' with the bill. He revealed that a "popular commentator" who hadn't seen the bill pledged to "destroy" him if he tried to move forward with it during an election year.

Sinema bashed Republicans for changing their tune on border security once the bill's text was released, criticizing her colleagues who wouldn't move forward with the legislation and declaring that "partisanship has won."

"We produced a bill that finally, after decades of no talk and no action, secures the border and solves the border crisis," Sinema said. "But less than 24 hours after we released the bill, my Republican colleagues changed their minds. Turns out, they want no talk and no action. It turns out border security is not actually a risk to our national security, it's just a talking point for the election."

Sen. Chris Murphy, a Connecticut Democrat and the third border negotiator, likewise bashed political dynamics at play, while noting that he still supports a supplemental funding package without the border components he helped negotiate. 

"The American people want us to solve tough problems like fixing the broken asylum system, and it's shameful Republicans would rather yell about the border on cable news than pass legislation," Murphy said in a statement. "But the future of global stability and desperately needed humanitarian aid hangs in the balance, so I am ready to pass a supplemental funding bill with or without the border provisions."

Nikole Killion and Alan He contributed reporting. 

Kaia Hubbard

Kaia Hubbard is a politics reporter for CBS News Digital based in Washington, D.C.