Senate negotiators have been striving for weeks to finish a carefully negotiated compromise on border and immigration policy that is meant to tamp down the number of migrants who come to the U.S. border with Mexico. But now that negotiations have dragged for weeks, election-year politics and demands from Trump are weighing it down.

At stake is a plan that President Biden and Senate Republican Leader Mitch McConnell of Kentucky have worked for months to broker in hopes of cajoling Congress to approve wartime aid for Ukraine. The U.S. has run out of money to supply Ukraine, potentially leaving the country stranded without robust supplies of ammunition and missiles to fend off Russia’s invasion.

In a closed-door Republican meeting Wednesday, McConnell acknowledged the reality of Trump’s opposition, that he is the party’s likely presidential nominee and discussed other options, including potentially separating Ukraine and the border as issues, according to two people who spoke anonymously to discuss the private meeting. Punchbowl News first reported the remarks.

McConnell’s comments raised fresh doubts in the Senate about his level of commitment to the border deal, though advocates for moving forward countered that the leader’s remarks were being misinterpreted.

“We’re still working on it,” McConnell told reporters Thursday morning.

He also reassured the conference at a Republican luncheon Thursday that he still personally supports pairing the border and Ukraine, said Sen. Mike Rounds (R-S.D.).

Oklahoma Sen. James Lankford, the head GOP negotiator, said the group is still working on the package. He said that McConnell was advocating for the proposal while simply acknowledging the political reality that the presidential primary season is fully underway.

“I think that’s the shift that has occurred, that he’s just acknowledging,” Lankford said. “That’s just a reality.”

Lankford has been working with a small bipartisan group and White House officials to try to close out the border deal. But release of the legislation has been held up by haggling over the price of the new policies and continued disagreements over limiting the president’s ability to allow people into the country under special circumstances, such as fleeing war and unrest.

“We’re really focused on making sure we get the bill out and that we get it through the Senate,” said Sen. Kyrsten Sinema, an Arizona independent who has been central to the talks.

White House spokeswoman Olivia Dalton told reporters aboard Air Force One on Thursday that the Biden administration has been working with the negotiators “in good faith,” feels that progress has been made, and hopes it will continue.

“We’re at a critical moment, and we’ve got to drive hard to get this done,” said South Dakota Sen. John Thune, the second-ranked Senate Republican. “If we can’t get there, then we’ll go to plan B.”

But congressional leaders have not identified any other way to push wartime funding for Ukraine. Scores of House Republicans are unwilling to send more money to the fight, even as longtime party stalwarts, like McConnell, have tried to convince them that preventing Russian President Vladimir Putin’s advance in Europe is directly in America’s interest.

“We know that if Putin prevails in Ukraine, the consequences for Western democracy and for the American people will be severe, and haunt us for years,” said Senate Majority Leader Charles E. Schumer of New York. “Democrats are also resolute on reaching an agreement on securing the southern border.”

Trump has loomed large over the talks, first skewering American support for Ukraine and now potentially upending a political compromise on the border that would hand his likely opponent, Biden, new policies meant to contain the historic numbers of migrants making their way to the country. With Republicans continuously raising the issue on the campaign trail, the border will probably remain central to elections this year.

Although many in Congress are anxiously awaiting the bill text, Trump has already said on social media that there should be no bipartisan border deal “unless we get EVERYTHING needed to shut down the INVASION of Millions & Millions of people.”

The lead Democratic negotiator, Connecticut Sen. Christopher S. Murphy, said he still has hope that Republicans will decide to accept the compromise — even though Democrats didn’t want to tie Ukraine aid and border security together in the first place.

“A lot of Republicans have become used to this being just merely a political issue, not an actual policy problem,” Murphy said. “And that’s hard for them to get over. But there is a big group of Senate Republicans who do want to solve the problem.”

Seeking to hold off objections from Trump, Republican senators have argued that the policies under discussion would not have an immediate effect on problems at the border and would even give Trump greater border enforcement authority if he is reelected.

“The issue will still be a live issue and I’d think it’d be one of the defining issues in the campaign,” said Sen. John Cornyn, a Texas Republican. “So we need to do our job here.”

But this week, a vocal contingent of Republicans have raised objections, including with heated exchanges during a closed-door Republican lunch Tuesday, according to several senators in the meeting. They have argued that presidents already have enough authority to implement hard-line border measures and Trump should have his say.

“If we expect him to be able to secure the border, he ought to be able to see this bill, and he ought to be able to be engaged and say, is this going to help me secure the border or not,” said Sen. Rick Scott, a Florida Republican, at a Wednesday news conference. “What we know is, he doesn’t need it.”

Sen. J.D. Vance, an Ohio Republican who is a Trump ally, said he spoke with the former president about the deal last week and he expressed worry that it would be “too weak.”

“When it fails, as it will, it allows the president to blame quote, unquote ‘MAGA Republicans’ for the failure of a border security package when in reality what failed was a very weak border security package that didn’t actually do anything,” Vance said.

But some Republicans worried walking away from an opportunity to enact border policy could backfire.

“If we were given an opportunity, and we decided for political purposes not to do it, yeah, I think we could be in serious trouble,” said Rounds. “A lot of our candidates could be in serious trouble back home.”

Associated Press writers Kevin Freking and Seung Min Kim contributed to this report.