WASHINGTON — Bipartisan talks to reach a border security agreement have stalled, lawmakers and aides said on Sunday, imperiling efforts to prevent another government shutdown days before the Friday deadline.
Senator Richard C. Shelby of Alabama, the Republican chairman of the Senate Appropriations Committee and a key figure in the negotiations, confirmed the impasse on Sunday, saying that he was “not confident we’re going to get there.”
“I’ll say 50-50 we get a deal,” Mr. Shelby said, speaking on “Fox News Sunday.” “The specter of a shutdown is always out there.”
The 17 House and Senate lawmakers negotiating, known as a conference committee, had set an informal deadline of Monday to reach a deal, because Congress would need that much time to consider the legislation without waiving procedural rules and still pass it by Friday, when funding for several departments and agencies expires.
But an aide familiar with the talks said lawmakers had stopped communicating, hung up primarily over Democrats’ demand for a hard limit on the number of beds given to Immigration and Customs Enforcement for housing detained immigrants already in the country.
President Trump, weighing in on Twitter, blamed Democratic leadership for the impasse.
“I don’t think the Dems on the Border Committee are being allowed by their leaders to make a deal,” he wrote. “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!”
While Democrats refused to entertain the prospect of fulfilling Mr. Trump’s $5.7 billion demand for a border wall, lawmakers had grown closer to accepting a number between $1.3 billion and $2 billion for physical barriers.
But they also demanded the limit on ICE beds, as a way to force the agency to focus on detaining migrants with criminal records instead of people who have overstayed their visas.
Democrats want a cap at 16,500, which would fold into an overall existing cap of 40,520 already funded in the spending bill for the last fiscal year.
But Republicans balked at the limitation, refused to accept the latest offer from Democrats and have yet to offer a counteroffer, according to an aide familiar with the negotiations.
“How in the world after that speech does he sign a bill that would reduce the bed spaces available for violent offenders?” said Senator Lindsey Graham, Republican of South Carolina and a close ally of the president, referring to Mr. Trump’s State of the Union address.
Speaking on “Sunday Morning Futures” on Fox News, he added, “He can’t do that, he won’t do that and you can take that to the bank.”
Still, Mr. Shelby and Senator Jon Tester, Democrat of Montana and a member of the conference committee, said on Sunday that they had not given up on reaching a deal. Democratic conferees held a conference call on Sunday morning to discuss options, according to a Democratic aide, but did not settle on a final decision on how to move forward.
The breakdown in negotiations came as Pentagon and administration officials were preparing for two situations: another partial government shutdown or the president, unsatisfied with an agreement produced by the bipartisan panel, fulfilling his threat to declare a national emergency.
Mr. Trump has told allies that while he would grudgingly accept a border security figure of about $2 billion, he was still considering using his executive authority to declare an emergency.
“The Wall will get built one way or the other!” Mr. Trump wrote on Twitter on Saturday afternoon.
In what one Defense Department official described as a surreal scramble over the weekend, Pentagon officials met on Friday and over the weekend to identify which Army Corps of Engineers construction projects would be tapped for money to help build Mr. Trump’s wall if the president declared a national emergency.
Officials pored over the language of multiple draft declarations that Mr. Trump might invoke if a deal is not reached or he rejects what lawmakers agree upon. Mr. Trump’s top national security aides — the so-called principals committee — are scheduled to meet on Monday to discuss that matter. Mr. Trump is then to convene a full National Security Council meeting on Tuesday, officials said.
If Mr. Trump declares a national emergency to build the wall, critics are expected to file suit in court to block construction and halt any funds shifted to the project. Democratic lawmakers, particularly in the House, are also preparing legislation that would limit the president’s ability to do so.
To stave off a court challenge, one proposal circulating among some White House officials, including those close to Stephen Miller, the president’s top domestic policy adviser, is to claim that the wall would be built to protect the more than 5,000 active-duty troops now operating near the southwestern border or deploying there soon.