The White House formally asked lawmakers Sunday to provide an additional $7 billion beyond what Senate appropriators proposed in their bipartisan Homeland Security spending bill last year, with more than half earmarked for a “steel barrier” along the southwest border.

The request, outlined in a letter from Acting Office of Management and Budget Director Russell Vought, doesn’t seem likely to lead to an immediate breakthrough in reopening large portions of the federal government that have been closed since Dec. 22.

At $5.7 billion for border barriers, or $4.1 billion more than the Senate’s fiscal 2019 bill, President Donald Trump proposes more than he’d requested earlier for a concrete wall. And the proposal reiterates some of Trump’s earlier requests rejected by Senate appropriators, including nearly $800 million to support 52,000 detention beds for immigrant detainees.

But the letter shows White House openness to Democratic priorities, including $800 million to respond to the “urgent humanitarian needs” of migrants taken into custody, as well as restoring the Obama-era Central American Minors program so asylum-seeking children can be screened in their home countries.

The OMB letter fleshes out the administration’s position as the partial government shutdown heads toward the longest in history. Negotiators met behind closed doors Sunday to discuss the proposals, with no evident signs of progress as the two sides dug in publicly over border security.

Like a separate discussion held Saturday, the meeting took place without the presence of Trump, who left earlier in the day for his Camp David retreat, or congressional leaders from each party. Officials from both parties said no agreement was reached.

Watch: What really happens during a government shutdown, explained

Trump nonetheless tweeted Sunday evening that it was a “productive meeting” and emphasized that he was no longer insisting on a concrete wall, which the White House views as a concession to Democrats. “Good solution, and made in the U.S.A.,” Trump wrote of the steel slats he’s considering.

Homeland Security Secretary Kirstjen Nielsen laid out a detailed breakdown of the administration’s $5.7 billion border barrier request to the assembled leadership and appropriations aides from both parties, according to a House GOP leadership aide.

A Democratic official countered that not enough information was provided, however, even after the meeting started 45 minutes late in order for the administration to round up additional materials. The official also said it wasn’t clear what other DHS programs would be cut to make room for such an increase.

“No progress was made today. At this time, there is not another meeting of this group scheduled,” the Democratic official said.

Acting White House Chief of Staff Mick Mulvaney said an interview aired earlier Sunday he saw little hope of a speedy resolution to the partial government shutdown.

Mulvaney said Democrats have refused to accept administration statistics outlining the threat to border security posed by criminals. “If you can’t even have a basic understanding of the facts, it’s going to be very hard to come to an agreement,” he said on CNN’s “State of the Union.”

While the White House is willing to negotiate, he said, “The Democrats, for better or worse, think they are winning this battle politically” and have shown no willingness to compromise.

But Trump himself didn’t seem in the mood for compromise before heading off to Camp David on Sunday: “There’s not going to be any bend right here,” he told reporters.

Democrats have been pressing the argument to reopen the government first, and then continue the negotiations. “I can tell you first that there’s no requirement that this government be shut down while we deliberate the future of any barrier, whether it’s a fence or a wall,” Senate Minority Whip Richard J. Durbin, D-Ill., said on CBS’ “Face the Nation.”

Tax refunds, parks cleanup

The House plans to take up individual spending bills starting with the Financial Services measure — identical to one the House passed last week as part of a larger package — which if enacted would open the IRS back up in time for tax-filing season and ensure refunds go out on schedule.

The chamber also plans to take up a separate Interior-EPA bill, also passed last week, which funds the National Park Service. Parks have been closed due to staff furloughs, though the administration has begun using fee collections to re-start services such as trash collection and restroom cleanup, according to a letter Sunday from Acting Interior Secretary David Bernhardt to Sen. Steve Daines, R-Mont.

Democrats questioned whether the administration had the authority to carry out the parks move, which was first reported by the Washington Post. In a statement, House Natural Resources Chairman Raúl M. Grijalva, D-Ariz., said his panel “will demand answers about whether these moves are legally justified.”

Durbin couldn’t give a timetable on when the government would open back up: “I can’t say that we’re close because the president’s made it clear he doesn’t care.”

Saturday’s negotiating session suggested talks “are going to drag on a lot longer,” Mulvaney said on “Meet the Press.”

“We had a two-hour meeting over whether or not a 20-foot-high, 30-foot-high steel bollard, steel slat barrier is a wall or not,” Mulvaney said. “That’s how broken I think some of these discussions are.”

Longest ever?

Sunday marked the 16th day of the shutdown, which began Dec. 22. That will tie the second-longest shutdown in the modern era of funding lapses, which began in 1980 with legal determinations that agencies couldn’t operate without appropriations.

If the stalemate drags on past Friday — which is an important pressure point because that is the date affected federal workers would miss their first paychecks if the government remains closed — it would become the longest shutdown, eclipsing the 21-day lapse that ended in early January 1996.

Senate Appropriations Chairman Richard C. Shelby, R-Ala., expressed frustration earlier Sunday that the matter hasn’t been resolved yet. “We could settle it. We should. But this has become a political circus,” Shelby said on Fox “Sunday Morning Futures.”

Shelby said the prospect of some 800,000 federal workers missing their paychecks would “have a profound effect” and that it ought to drive the parties to compromise. “I hope it’s pressure on both sides,” he said, while adding that he’s unsure of what exactly the Democrats want.

“You’re going to have to give the Democrats something, but right now they’re against everything,” Shelby said.

Trump said Sunday that his patience may run out soon and start using existing authorities to finance portions of the wall.

“I may decide a national emergency depending on what happens over the next few days,” Trump said. “The shutdown could end tomorrow, or it can go on for a very long time,” he said. “It’s really dependent on the Democrats.”

It’s not clear what authorities to build the wall the administration would use, but one avenue could be a military construction authorization law enacted in 1982 that provides “construction authority in the event of a declaration of war or national emergency.” The statute says such an event would require use of the armed forces, and the construction project would have to be “necessary to support such use of the armed forces.”

Another possibility is anti-narcotics trafficking legislation codified as part of the fiscal 2017 defense authorization law, which allows the Secretary of Defense to “provide support” for activities including “construction of roads and fences and installation of lighting to block drug smuggling corridors across international boundaries of the United States.”

Senate Armed Services ranking member Jack Reed, D-R.I., said last week Congress could block the use of such authorities, arguing it would take money away from more pressing military construction and housing projects.

“The President needs to understand that there is bipartisan opposition to misusing defense dollars or treating the Pentagon like a campaign piggy bank,” Reed said in a statement.

Shelby said he didn’t know if Trump would attempt to use such authorities. “I believe the president has got a lot more power to defend this country as commander in chief than people realize,” he said. But Shelby stressed that the way to “do it right” is for Congress to act. “We’ve got to get together and put America first,” he said.

A few Republicans, such as Susan Collins of Maine, are starting to push for reopening government quickly while talks continue. She said on “Meet the Press” that the Senate should take up the $272.4 billion, six-bill spending package that the House passed last week.

Collins also said she could envision a compromise pairing $2.5 billion for border security improvements with a path to citizenship for so-called Dreamers, who were brought to the country illegally as children.

Collins is up for re-election in 2020. While she won her last election with 67 percent of the vote, the state generally leans Democratic and former Rep. Bruce Poliquin, R-Maine, who represented the more GOP-leaning of the state’s two districts, was defeated in last November’s midterm races.

Paul M. Krawzak, Niels Lesniewski, Lindsey McPherson, Jael Holzman and John T. Bennett contributed to this report.