WASHINGTON — The nation faces the real possibility of another government shutdown Friday at midnight, as bipartisan talks aimed at averting that outcome broke down in a dispute over immigration enforcement, lawmakers and aides said Sunday.

President Donald Trump’s border wall demands, which precipitated the record-long 35-day shutdown that ended late last month, were a secondary issue in the impasse that developed over the weekend, according to lawmakers and aides in both parties.

Instead negotiations collapsed over Democrats’ insistence on limiting the number of unauthorized immigrants who can be detained by the U.S. Immigration and Customs Enforcement agency. The breakdown in talks made it unlikely that lawmakers will be able to finalize an agreement today, as they had hoped to do so it could pass the House and Senate before Friday night’s deadline.

“I think the talks are stalled right now,” Senate Appropriations Committee Chairman Richard Shelby of Alabama, the lead Republican negotiator, said on Fox News Sunday. “I’m not confident we’re going to get there.”

The stalemate left the path forward to keeping the government open unclear. It was unclear when or if formal negotiations will resume.

The Homeland Security, State, Agriculture and Commerce departments and a number of other federal agencies are currently operating on a stopgap spending bill that Trump signed Jan. 25. There’s little appetite for another short-term funding extension, but without some action by midnight on Feb. 15, those agencies will run out of money and begin to shut down again.

The president, who is holding a rally in El Paso, Texas, tonight that’s likely to focus on his demands for more border security, referred to the disagreement in a tweet on Sunday. “I don’t think the Dems on the Border Committee are being allowed by their leaders to make a deal. They are offering very little money for the desperately needed Border Wall & now, out of the blue, want a cap on convicted violent felons to be held in detention!” the president wrote.

Lawmakers had been trading offers over how much money could go to barriers along the U.S.-Mexico border, and were looking at a range between $1.3 billion and $2 billion, far short of the $5.7 billion Trump had demanded. The White House had begun to signal flexibility on that issue, even though Trump would end up with much less money than he sought, and the enhanced fencing or other barriers agreed to by Congress would fall short of the 200-plus miles of steel walls he’d wanted.

But throughout the talks, Democrats had also been focused on limiting ICE’s ability to detain unauthorized immigrants, which has become a major issue for the party because of their opposition to the Trump administration’s aggressive detention tactics. The Democrats’ proposal included a new limit on detention beds for immigrants picked up not at the border, but in the interior of the country.

Democrats wanted to cap that number at 16,500, which they said is around the level of interior detentions in the final years of the Obama administration. Republicans proposed excluding immigrants with criminal records from the cap. But Democrats said that would make the cap toothless, because it would amount to giving ICE free rein to round up thousands of immigrants without criminal records, on top of unlimited numbers of immigrants with criminal convictions.

On MSNBC Sunday afternoon, Rep. Katie Hill, D-Calif., defended the Democratic position on bed space and accused Republicans of misrepresenting the facts. “This news came from Republicans who have decided that their narrative is going to be that we’re trying to reduce beds for violent criminals, and that’s just not true,” Hill said.

Democrats, newly in control of the House, have faced pressure from some liberals in their ranks to draw a much harder line in their negotiations over the border. Liberals including Rep. Alexandria Ocasio-Cortez, D-N.Y., have proposed entirely cutting funding to ICE, and refusing any additional money for border barriers whatsoever.

Democrats on the bipartisan negotiating committee have resisted those demands. But Republicans quickly seized on the new dispute over detention beds to try to lump all Democrats in with the most liberal elements in the party.

“Now, apparently, not only is it enough they want to abolish ICE. They want to abolish the bed spaces available to the country to house violent offenders, so they can be held and deported,” Sen. Lindsey O. Graham, R-S.C., said on Fox News Channel. “I promise you this. Donald Trump is not going to sign any bill that reduces the number of bed spaces available to hold violent offenders who come across our border. He can’t do that. He won’t do that, and you can take that to the bank.”

The fight over how many immigrants can be detained at once became extremely problematic in recent days, just as the White House began signaling to negotiators that it would be more flexible on how much money Congress appropriated for a wall along the Mexico border.

White House officials have become increasingly confident that by declaring a national emergency, Trump will be able to redirect billions of dollars in other federal funding to be used for a wall or barriers. One scenario they had prepared for was for Congress to pass a bill appropriating some money for border security and then use the national emergency declaration to loosen even more funds.

This could draw legal challenges from Democrats, landowners and other groups, but White House officials and some external advisers have said it was the best way to proceed.

A total breakdown in talks poses a new set of challenges, however. It dramatically increases the odds of another partial government shutdown beginning Saturday. This would prevent roughly 800,000 federal workers from being paid indefinitely.

During the last shutdown, which began Dec. 22, the White House relied on hundreds of thousands of federal employees to continue coming to work unpaid for more than a month in order for key government services to continue, including Border Patrol agents, Secret Service officers, airport screeners, and air traffic controllers.

Many of the federal employees, however, refused to show up for work and called in sick, including airport screeners and Internal Revenue Service officers, and it’s unclear what they would do if there’s another shutdown. The IRS is in the midst of tax-filing season, and a major disruption could have huge implications for the ability of millions of Americans to obtain tax refunds in a timely fashion.

Though the odds of a government shutdown have increased markedly in the past 24 hours, negotiators have not said for certain that one will occur. That’s because even though there is less than one week left to complete a deal, they still have time to work something out, and often deadlines force legislators to compromise.

In the run-up to the last government shutdown, the odds of an impasse spiked markedly on the Sunday before the deadline, and then appeared to soften by Tuesday, when the White House walked back its demands.

On Dec. 19, Republicans felt confident that Trump would not lead them into a shutdown and unanimously agreed to a short-term funding bill. But by that night, Trump signaled to lawmakers that he would not support the agreement, and two days later they hit the deadline without an agreement.

“There are bumps in the road, but as long as we stay focused in a bipartisan way, bicameral way, to get this done, I’m hopeful we can get it done. Is it a done deal? No it isn’t, and we could end up in a train wreck, it’s happened before,” Sen. Jon Tester, D-Mont., one of the negotiators, said on Fox News Sunday. “But I don’t think anybody has an appetite for a government shutdown, and I think everybody wants to make sure our borders are secure.”