Republicans and Democrats are not communicating for now, imperiling the prospects for a deal as time runs short.
A congressional deal seemed to stall even after Mulvaney convened a bipartisan group of lawmakers at Camp David, the presidential retreat in northern Maryland.
The sticking point is over detention beds, both people said, an issue that would typically be regarded as a side-note to the broader talks on the level of funding for border security.
President Donald Trump is pushing back against criticisms that a leak of his private schedule suggests he is not working hard. If an agreement on funding the government isn't reached by Friday at midnight, the government could partially shut down again, just three weeks after the longest USA government shutdown in history. Negotiators had hoped to unveil a deal Monday to set up votes in the House and Senate before the deadline. "I'm not confident we're going to get there". "We've got some problems with the Democrats" over funding for U.S. Immigration and Customs Enforcement operations. "We're still participating, we're still listening, we're still talking, but we're not leading the negotiations". Richard Shelby, R-Ala., said Sunday on "Fox News Sunday". "There'll be some things that simply we couldn't agree to".
Acting White House chief of staff Mick Mulvaney hasn't ruled out another shutdown.
"We are not interested in our committee in whether he's a tax cheat or not worth what he says he is", Rep. Adam B. Schiff (D-Calif.) said in an appearance on the NBC's "Meet the Press".
Predictably each side blamed the other for the stall in negotiations.
Talks on border security funding collapsed after Democratic and Republican lawmakers clashed over immigrant detention policy as they worked to avert another USA government shutdown, a Republican senator said on Sunday. The shutdown was caused by his demand for border wall money - and Democrats' refusal to provide it.
The White House and many Republicans want to push the amount that would be spent for building physical barriers to $US2 billion ($A2.8 billion) or higher.
Democratic negotiators were hoping to cap the number of beds at 16,500.
"The government shutdown is technically still on the table; we do not want it to come to that but that option is still open to the president and will remain so", Mulvaney told "Fox News Sunday" viewers. Calls on the topic are expected today. Democrats want to limit the number of beds to force the Trump administration to prioritize arresting and deporting serious criminals, not law-abiding immigrants.
"I've seen the Democratic and the latest Republican offer ..."
Trump said on Twitter Sunday that he doesn't think Democrats on the committee are being allowed by their leaders to make a deal with border wall money and "now, out of the blue, want a cap on convicted violent felons to be held in detention!"
"I'll say 50-50 we get a deal", he said, adding: "The spectre of a shutdown is always out there".
Republican Senator Lindsey Graham, who is close to Trump, warned against limiting beds. The South Carolina Republican, a confidant of the president, said he would advise Trump "to take as much money as he can get [from Congress] and find the rest on his own".
Democratic negotiators proved stubborn as deliberations first began.
"Democrats have chosen petty games over the safety of Americans", the campaign said in the email.
"When we find that person or persons, and it's likely to be a career staffer, you're going learn a lot about how hard it is to fire federal workers", said Mulvaney.