The Trump White House maintained its hard line on funding for a border wall in a letter Sunday to congressional leaders, demanding $5.7 billion for construction of a barrier as the partial government shutdown heads into its third week after weekend talks.

The wall is “central to any strategy,” Russell T. Vought, acting director of the Office of Management and Budget, wrote, asking for funds for “234 miles of new physical barrier.”

But the two-page letter, which was obtained by The Washington Post, also provided new details on Trump’s position, which has largely consisted of ultimatums and tweets amid stalled negotiations with Democrats, by listing funding requests for his immigration agenda across the federal government.

Trump advisers said Sunday that the administration wrote the letter after Democratic congressional aides asked Vice President Pence, who led the weekend discussions at the White House, for specifics on budget estimates for the Trump administration’s priorities so that the negotiations could advance this week.

Lawmakers from both parties discussed on Jan. 6 how a deal could be reached to end the government shutdown. (Luis Velarde/The Washington Post)

“During our meetings with congressional staff this weekend, we made it clear that we have a crisis on our southern border, and we outlined the president’s plan to secure our border, build a wall, and protect the American people,” Pence said in a brief interview. “It’s time for the Democrats to start negotiating.”

Senior administration officials described the letter as a flicker of progress, in particular the request for “an additional $800 million to address urgent humanitarian needs” and unaccompanied migrant children arriving at the border, an issue they said Democrats have made a priority during the talks. The officials also said that the letter’s formal call for a “steel barrier” rather than a massive concrete wall — as Trump long promised — was another notable, if minor, development.

Still, both sides acknowledged that they remained far apart late Sunday, and while Democrats may be interested in negotiating a broader immigration deal that includes humanitarian funding, they have refused to do so unless the government is reopened — and House Speaker Nancy Pelosi (D-Calif.) has called the wall an “immorality.”

Democrats largely reacted to the letter with a shrug, and several senior aides described the letter as a summary of the weekend meetings rather than a breakthrough. “The Republicans remain boxed in with the wall,” said one aide who was not authored to speak publicly. “We can’t discuss everything else until the government reopens.”

The administration has also signaled that it would be willing to restore some version of an Obama-era program that allowed children in Central America to apply for U.S. asylum in their home countries, according to an official with knowledge of the proposal. The Central American Minors program, or CAM, was established during a 2014 border crisis, when unaccompanied minors were arriving in unprecedented numbers, often assisted by smugglers.

Trump canceled the program in 2017.

Restoring it has been a Democratic priority, but in exchange the administration said it wants changes to laws that protect underage trafficking victims, so as to ease restrictions on the government’s ability to deport teenagers and children.

Earlier Sunday, Trump met with White House staff at Camp David, where the president’s long-promised border wall was among the topics on the agenda.

The meeting came one day after Pence, top White House officials and senior congressional aides emerged empty-handed after more than two hours of negotiations on ending the stalemate.

“We’re looking at a national emergency because we have a national emergency,” Trump told reporters outside the White House upon returning Sunday evening. Before departing in the morning, he said he may act unilaterally to secure wall funding “depending on what happens over the next few days.”

In a bid to force Democrats’ hand, Trump has said that he is considering declaring an emergency to begin wall construction without congressional approval. The legality of such a move is unclear, however, and the president would almost certainly face immediate legal challenges in the courts.

Trump also said Sunday that he understood the predicament facing hundreds of thousands of federal workers who are not receiving their paychecks.

“I can relate, and I’m sure the people who are on the receiving end will make adjustments; they always do,” Trump said. He claimed that “many of those people agree with what I’m doing”: refusing to reopen the government without obtaining funding for his long-promised border wall.

And he further backed away from the notion of a concrete wall, telling reporters that he has informed his staff to now say “steel barrier.” During the 2016 campaign, Trump often pledged to build a concrete wall, but on Sunday, he argued that steel slats “will be less obtrusive and stronger.”

“They don’t like concrete, so we’ll give them steel,” he said of congressional Democrats.

While Trump was meeting with staff at Camp David, Pence met again with congressional leadership staff. In a tweet Sunday night, Trump sought to put a positive spin on the meeting, describing it as “productive” and declaring that “we are now planning a Steel Barrier rather than concrete.”

But a Democratic official familiar with Sunday’s meeting with Pence said no progress had been made and that Democratic staff had yet to receive a full budget justification for the president’s $5.7 billion demand.

Democrats on Sunday “pleaded again for the White House to change course and reopen government” by backing funding measures that have been passed by the House and have bipartisan support in the Senate, but Pence “said the president would not do that,” according to the official, who was not authorized to speak publicly about the talks.

No further meetings have yet been scheduled.

On Saturday, Pence refused to budge from the more than $5 billion Trump has demanded from Congress to pay for a portion of the wall, according to two Democratic officials briefed on the negotiations.

The standoff — which has heavily affected national parks and other operations and threatens to halt payments as varied as food stamps and tax refunds — has made Trump’s unrealized border wall the linchpin of his presidency as he seeks to make good on a signature campaign promise.

The administration’s proposal on “humanitarian needs” comes after an unprecedented surge in the number of migrant families crossing the border.

In recent months, so many Central American parents have arrived with children that Border Patrol stations have become dangerously overcrowded and unhealthy. Two Guatemalan children died in December after being taken into custody by U.S. agents.

Pence and Homeland Security Secretary Kristjen Nielsen made a presentation on this issue over the weekend, officials said.

The $800 million would alleviate what homeland security officials characterize as a “humanitarian crisis” by setting up temporary facilities where families would have better access to doctors and food in a more comfortable setting than the cement-floor holding cells of border stations where they are currently held.

Nielsen and Kevin McAleenan, the commissioner of U.S. Customs and Border Protection, have pushed hard to include the $800 million, according to an official with knowledge of the discussion who spoke on the condition of anonymity. “They went to bat for this,” the official said, viewing the proposal as a significant concession to Democratic demands for better treatment of detained migrants.

Immigration hard-liners have been loath to spend significant funds on improving detention conditions, and such temporary facilities would probably be derided as “welcome centers” at a time when record numbers of migrants are bringing children with them. As a result of court rulings that limit the amount of time minors can be held in detention, a parent who brings a child has a far better chance of avoiding a prolonged detention and deportation.

Instead, with more than 2,000 migrants crossing the border each day, U.S. immigration authorities have resorted to mass releases, because they cannot transport and process the families fast enough, and so many children are falling ill in government custody.

The partial shutdown over wall funding — leaving U.S. border agents working long hours without pay — has only added to the strain.

Pelosi, in her first sit-down interview on network television since reclaiming the speaker’s gavel last week, blasted Trump for suggesting that he may unilaterally move to build the border wall.

“The impression you get from the president [is] that he would like to not only close government, build a wall, but also abolish Congress so the only voice that mattered was his own,” Pelosi told Jane Pauley in the interview, which aired on CBS News’s “Sunday Morning.”

Democrats plan to use their new House majority this week to continue pressing Trump for a resolution. House Appropriations Chair Nita M. Lowey (D-N.Y.) on Sunday released the text of four bills that would reopen key parts of the government and ensure back pay for federal workers who have been furloughed during the shutdown.

“After we pass these four bills, the Senate should clear them and the President should sign them into law,” Lowey said in a statement.

Trump’s consideration of using emergency powers was hotly debated by those on both sides of the issue on the Sunday morning news shows.

Mick Mulvaney, the acting White House chief of staff, defended Trump on CNN’s “State of the Union,” arguing that the president has “a great deal of latitude over how the government is run.”

House Armed Services Committee Chairman Adam Smith (D-Wash.) said that while Trump may have the power to act unilaterally, doing so is likely to open him up to legal challenges.

But House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) said Trump’s words were just “threatening talk” with no power behind them. After bowing to his base and refusing to compromise with Democrats, Schiff said, Trump needs to “figure out how he unpaints himself from that corner.”

Democrats also took aim at Senate Majority Leader Mitch McConnell (R-Ky.), who has been uncharacteristically disengaged from the shutdown talks as Trump has repeatedly shifted course. McConnell pushed a short-term funding bill through the Senate before Christmas, but Trump abruptly announced the next morning that he would not support the measure.

On CBS News’s “Face the Nation,” Senate Minority Whip Richard J. Durbin (D-Ill.) called for McConnell to “step up and join” the negotiations rather than sit on the sidelines.

Sen. Lindsey O. Graham (R-S.C.), a key congressional ally of Trump, suggested on CBS that the president would be open to a compromise that includes wall funding in return for protections for “dreamers,” immigrants brought to the United States illegally as children, and others with temporary protected status.

Trump said at a Rose Garden news conference on Friday that he wants to see how the Supreme Court rules on the Deferred Action for Childhood Arrivals program, which had provided work permits to “dreamers,” before including the issue in any talks.

He told reporters on Sunday that he “would consider DACA” but would rather wait until the high court rules.

Karoun Demirjian, Seung Min Kim and Anne Gearan contributed to this report.