WASHINGTON — Key Senate negotiators say they’ve struck a tentative deal to enact tougher U.S. immigration and asylum laws, marking a significant breakthrough on a politically explosive issue as the 2024 election year gets underway.

But the pact is in jeopardy even before senators release the text of the bill, which they’re hoping to do in the coming days in anticipation of voting on it beginning next week.

Senate Majority Leader Chuck Schumer, D-N.Y., said Thursday that senators plan to release the “full text” of the immigration package, which will include aid funding for Ukraine and Israel, “as early as tomorrow” and “no later than Sunday.”

“That will give members plenty of time to read the bill before voting,” he said, adding he plans to hold the first procedural vote on the package “no later than Wednesday.”

The tentative agreement, struck by Sens. James Lankford, R-Okla., Chris Murphy, D-Conn., and Kyrsten Sinema, I-Ariz., represents an ambitious effort to tackle a problem that has bedeviled Congress for decades — in the middle of an election year.

“For all intents and purposes, we have an agreement,” Murphy said.

The measure faces uncertainty in the Senate, pushback from House Speaker Mike Johnson, R-La., and a steady bombardment of opposition from likely GOP presidential nominee Donald Trump that is endangering Republican support. Some in the party worry that it could give President Joe Biden a victory on a political vulnerability in his 2024 re-election bid.

“I feel like the guy standing in the middle of the field in a thunderstorm holding up the metal stick currently,” Lankford said, adding that process has been “really intense.”

Lankford maintained that he had kept Johnson informed of the scope and details of the border bill throughout the process, keeping the speaker’s staff in the loop throughout the final stages.

But Johnson’s office pushed back on Lankford’s characterization of the discussions, telling NBC News in a statement: “Senator Lankford nor his office has never provided Speaker Johnson’s office with proposed legislative text or a written description of the new expulsion authority. They have described it in conversation with less detail than what is available in published news reports.”

The deal would take a three-pronged approach to mitigating the chaos at the border. First, it would limit options for people outside the U.S. to pursue asylum. Second, it would raise the standard for people at the border to qualify for asylum. Third, it would speed up processing of claims, cut off avenues for appeal if they are rejected, and end “catch and release” by enforcing government monitoring of migrants throughout the process.

Sen. Kevin Cramer, R-N.D., said he’s favorably inclined to support it but said the prospects of getting a majority of the Senate GOP on board is “declining,” as some senators prefer not to “walk the plank” for a complicated bill if it is unlikely to clear the House.

“The path is getting narrower to get to 25,” Cramer said.

The bill needs 60 votes to break a filibuster in the Senate. But Sen. Thom Tillis, R-N.C., a proponent of the deal, said it’s unlikely to move forward without the support of at least half the Republican caucus, or 25 senators.

One holdup to releasing the text is securing enough funding to implement the policy changes.

“I’m getting worried,” Murphy told reporters on Thursday. “Republicans have to be serious about funding the deal that we have made. Our policy deal is done but it requires the bill to fund the changes that Republicans asked for.”

Another reason for the delay is that Senate Minority Leader Mitch McConnell, R-Ky., has been speaking to his members to make sure there’s enough support when the bill is released, according to a source with knowledge of the talks, so that it won’t have to be changed after the fact to accommodate conservative concerns. (McConnell’s office declined to comment.)

Further complicating matters, House Republicans are preparing to impeach Homeland Security Secretary Alejandro Mayorkas, accusing him of refusing to enforce immigration laws even as he has met with the Senate negotiators to discuss the new deal.

In the meantime, Senate negotiators have been playing whack-a-mole with a steady stream of claims about the contents of the bill on conservative media, which have sparked a backlash based on assertions the senators insist are inaccurate.

In a rare gaggle with reporters on Wednesday, Sinema defended the emerging deal and rebuked Republican “misrepresentation” of the bill, calling comments made by hard-liners — including Johnson as recently as Wednesday — “factually incorrect.”

“The rumors that are swirling about what this legislation does are wrong,” she said. “Our bill ends ‘catch and release.’ It ensures that the government both has the power and must close down the border during times when our system is overwhelmed. And it creates new structures to ensure that folks who do not qualify for asylum cannot enter the country and stay here.”

The pressure placed on Senate Republicans by Trump and Johnson, backed by a contingent of hard-right senators, could torch the deal and quash hopes of approving critical aid to Ukraine, Israel and Gaza refugees. It was the focal point of an extensive discussion among Senate Republicans during a closed-door lunch on Wednesday, but no concrete decisions were made, according to multiple Senators leaving the meeting.

“We had a lot of discussion, obviously about the border around here, but it’s important to focus on the other rationale for the supplemental: We’ve got two friends in the middle of a huge fight, Israel, Ukraine. They need help,” McConnell, a staunch supporter of helping Ukraine fend off Russia, told reporters on Wednesday.

“And hopefully,” McConnell said, “we can work this border issue out in a way that is satisfactory but there’s bipartisan support here in the Senate for both Israel and Ukraine. And hopefully, at some point, we’ll get them the help that they need.”

The negotiations have occurred in fits and starts, collapsing around Thanksgiving before restarting as Democrats decided they were willing to pay a price to get Ukraine aid.

They were also complicated by Democrats’ concerns that new executive powers without constraints could be abused by Trump or a future president like him. It’s why negotiators put a provision in the legislation that would cap the number of days the border could be shut down under a new authority that would close the border when encounters exceed a daily average of 5,000.

The legislation is likely to lose the votes of a contingent of progressive and Congressional Hispanic Caucus members, who argue that Democrats are conceding too much to the GOP without securing their priorities, such as normalizing the status of young “Dreamers” who were brought to the U.S. illegally as children.

The bill would significantly change the way migrants are “paroled” at the border, effectively ending the status quo. “It was troubling to me that it was even on the table,” said a senior member of the Hispanic Caucus. 

But many Democrats are supportive of tightening immigration laws, and the aid to Ukraine is an added incentive to get them on board. The main obstacle to turning the deal into law is conservative blowback.

“Some people say I want you to do it differently. And my statement is: Great, go jump in and negotiate it,” Lankford said. “If we can actually make that law rather than just a press conference, please go negotiate it. My job is to go make law.”