The White House on Sunday officially asked Congress for $5.7 billion to build a “steel barrier,” confirming that President Donald Trump was backing down from his call for a concrete wall along the U.S.-Mexico border.

The request, made against the backdrop of a partial government shutdown that has entered its third week, comes as Trump is also considering whether to go around Congress and declare a national emergency in order to construct his proposed wall.

“A physical barrier — wall — creates an enduring capability that helps field personnel stop, slow down, and/or contain illegal entries,” Russ Vought, the acting director of the Office of Management and Budget, wrote in letters sent on Sunday to the House Appropriations Committee chairwoman, Rep. Nita Lowey (D-N.Y.), and its ranking member, Rep. Kay Granger (R-Texas).

Just hours earlier, the president had again threatened to declare a national emergency as a means for construction, even while saying that he would first gauge the results of upcoming negotiations to end the shutdown, which was triggered by partisan debate over his signature campaign promise.

“I may decide a national emergency depending on what happens over the next few days,” Trump told reporters as he exited the White House en route to Camp David, according to a pool report.

“We have to build the wall or we have to build the barrier. The barrier or the wall can be of steel instead of concrete if that works better,” the president said.

Trump’s insistence on a border wall comes as the newly Democratic-controlled House asserts its power. Last week, the House passed legislation that would reopen the federal government. In addition to trying to fund the government without giving the president his wall, House Democrats are signaling that they’re ready to go after him in other ways, by requiring that he release his tax returns and providing transcripts of congressional testimony to special counsel Robert Mueller for the Russia investigation.

Top congressional aides met Sunday afternoon with the Trump administration for another round of talks, as the shutdown entered its 16th day. In a tweet just before 5 p.m. Sunday, the president appeared to communicate that the day’s deliberations between Democratic staffers and White House liaisons had concluded, yielding more progress than a similar conference on Saturday.

“V.P. Mike Pence and group had a productive meeting with the Schumer/Pelosi representatives today,” Trump wrote online, referring to Senate Minority Leader Chuck Schumer (D-N.Y.) and House Speaker Nancy Pelosi (D-Calif.). “Many details of Border Security were discussed.”

The president also reaffirmed his commitment to a fortification made of steel instead of a concrete bulwark, tweeting: “We are now planning a Steel Barrier rather than concrete. It is both stronger & less obtrusive. Good solution, and made in the U.S.A.”

But a Democratic official familiar with the meeting said that the White House neglected to provide “a full budget justification” at the meeting for its $5.7 billion wall request and that no progress was made.

According to the official, Democratic staff asked that the White House reopen the government by supporting legislation passed by the House last week, but that Pence responded that the president would not accept such a proposal.

In addition to $5.7 billion for a steel barrier, the Trump administration’s letter on Sunday asked for more money than the Senate bill for fiscal year 2019 allocates for other border security measures. Those include the hiring of additional border patrol agents as well as law enforcement personnel working for Immigration and Customs Enforcement. The administration also requested more money for detention beds and for technology to better equip Customs and Border Protection “to deter and detect more contraband.”

Arriving back in Washington on Sunday afternoon, Trump told reporters that the administration would be pursuing the “steel barrier,” in what he described as a concession to Democrats on Capitol Hill.

“I informed my folks to say that we’ll build a steel barrier,” Trump said, according to a pool report. “It’ll be less obtrusive and it’ll be stronger.”

He added: “They don’t like concrete, so we’ll give them steel.”

But Democratic lawmakers have thus far not publicly suggested that the wall’s building material would factor into their final decision to support or oppose the structure, and the president has previously reneged on deals with the party’s leaders in other contentious funding fights as recently as March 2018.

Democrats appeared to disagree Sunday on whether the president actually had the authority to build a wall without congressional approval under the premise of a national emergency.

Rep. Adam Smith (D-Wash.), chairman of the House Armed Services Committee, acknowledged that Trump had the authority to do so, but said he would likely be met with a lawsuit.

“There is a provision in law that says the president can declare an emergency,” Smith said Sunday on ABC’s “This Week with George Stephanopoulos.” “In this case, I think the president would be wide open to a court challenge saying, where is the emergency? You have to establish that in order to do this.”

But Rep. Adam Schiff (D-Calif.), chairman of the House Intelligence Committee, disagreed.

“I make of that really threatening talk from the president that he doesn’t have the power to execute,” Schiff said in an interview with CNN’s Jake Tapper. “Look, if Harry Truman couldn’t nationalize the steel industry during wartime, this president doesn’t have the power to declare an emergency and build a multibillion-dollar wall on the border. So, that’s a nonstarter.”

According to data from the U.S. Customs and Border Protection agency, there were396,579 arrests along the southwestern border in fiscal year 2018 — lower than the average number of 400,751 over the previous decade. The number of border arrests in 2018 was higher than in 2017, when there were 303,916 arrests.

If Trump were to build a wall under the premise of a national emergency, it would likely be challenged in court, similar to his other immigration policies, including his asylum ban.

Liberal groups were already quick to dismiss the notion that the president had the legal authority to declare a national emergency to fund the wall.

“What Trump is proposing is illegal, plain and simple,” the left-leaning Center for American Progress said in a memo sent to reporters Sunday. “It would be a flagrant abuse of military power and his most direct assault on the separation of powers and democracy to date.”

But some agree with Trump that a national emergency exists.

Jessica Vaughan, director of policy studies at the Center for Immigration Studies, which seeks lower levels of immigration, wrote in a text on Sunday that “the emergency is the major, growing influx of people who have heard about the catch and release policies for those arriving with children and claiming fear of return, and the inability of Congress to respond.”

Trump on Sunday also reiterated his arguments for the building of the wall and argued without supporting evidence that many of the government workers who are not receiving their paychecks are supportive of what he is doing.

“This is a very important battle to win from the standpoint of safety, No. 1, defining our country and who we are,” he said. “Also from the standpoint of dollars. This wall will pay for itself many times through the course of the year.”

The president’s remarks came as Mick Mulvaney, his acting chief of staff, said on CNN that Cabinet secretaries had been instructed to look for money within their budgets that could be used to pay for the wall. Mulvaney said he had “been working with all the Cabinet secretaries to try and find money that we can legally use to defend the southern border.”

Trump first indicated in a Friday news conference that he would consider using his emergency powers to bypass Congress and begin construction on the wall.

“Absolutely, we could call a national emergency because of the security of our county,” the president told reporters assembled in the Rose Garden at the White House.

“I haven’t done it. I may do it. I may do it. But we could call a national emergency and build it very quickly,” Trump said Friday, adding that he would prefer to acquire funding for the wall “through a negotiated process” with congressional lawmakers in a deal that would bring an end to the shutdown.

Although Trump administration and congressional aides met Saturday to discuss a solution to the partial government shutdown, little progress has been made and Congress remains out until Tuesday. Despite the absence of a deal, Mulvaney reiterated to Chuck Todd on NBC’s “Meet the Press” on Sunday that the president was willing to give up his concrete wall.

“If he has to give up a concrete wall, replace it with a steel fence in order to do that so that Democrats can say, ‘See? He’s not building a wall anymore,’ that should help us move in the right direction,” Mulvaney said. When asked about Mulvaney’s comments, House Majority Leader Steny Hoyer (D-Md.) told “Meet the Press” that “it is an offer he made and it’ll be discussed.”

With the shutdown in its third week, lawmakers called for a quick solution. Also on “Meet the Press,” Sen. Susan Collins (R-Maine) described the debate over a steel or concrete wall as “rather bizarre.” She reiterated that she would like for Senate Majority Leader Mitch McConnell (R-Ky.) to bring House-passed legislation to the floor that would reopen the government, but noted that Schumer, Pelosi and Trump needed to come to a compromise.

“We can pass bills, but they won’t become law,” Collins said, adding that “both sides need to indicate a willingness to listen and to compromise.”

Burgess Everett, John Bresnahan, Ted Hesson and Victoria Guida contributed to this report.