WASHINGTON >> The record 35-day federal shutdown has ended with President Donald Trump giving in to mounting pressure and signing legislation to reopen the government for three weeks, a retreat from his demand that Congress commit billions to a U.S.-Mexico border wall before federal agencies could resume work.

Trump, in a weakened negotiating position, will try again to persuade lawmakers to finance the wall, with a Feb. 15 deadline looming as he holds out the potential of another shutdown. He tweeted Saturday that “21 days goes very quickly” and that making a deal “will not be easy” because both Republicans and Democrats are “very dug in.”

Without explaining how it would happen, the president asserted, “We will build the Wall!” even though the measure he signed into law Friday after reaching agreement with congressional leaders contained no new money for the wall. And House Speaker Nancy Pelosi, D-Calif., has said repeatedly she will not go for it: “Have I not been clear? No, I have been very clear.”

The administration asked department heads to reopen offices in a “prompt and orderly manner” and said hundreds of thousands of furloughed employees , whose latest missed payday had brought new urgency to efforts to resolve the standoff, could return to work. The deal includes back pay, which the administration promises to get out as soon as possible.

The shutdown ended as Democratic leaders had insisted it must, with the government first reopening and then talks about border security. Also, a strong majority of Americans blamed Trump for the stalemate and rejected his arguments for a border wall, recent polls show.

“The president thought he could crack Democrats, and he didn’t, and I hope it’s a lesson for him,” said the Senate Democratic leader, Chuck Schumer of New York.

Trump, nonetheless, tweeted, “This was in no way a concession” and said he wanted to help those “badly hurt” by the shutdown. The president also said, without elaboration, that if there is no “fair deal” with Congress by Feb. 15, “it’s off to the races!”

Earlier, in a Rose Garden speech when he announced the short-term agreement, Trump raised the prospect of using “the powers afforded to me under the laws and Constitution of the United States” to get what he wants.

The president has said he could declare a national emergency and use money under such a declaration to pay for the border wall unilaterally. Such a move would almost certainly face legal challenges.

A bipartisan committee of House and Senate lawmakers was being formed to consider border spending as part of the legislative process in the coming weeks.

Also to be determined is a new date for the president to deliver his State of the Union address, which was postponed from Jan. 29 during the shutdown.

As border talks resume, Senate Majority Leader Mitch McConnell, R-Ky., said he hopes for “good-faith negotiations over the next three weeks to try to resolve our differences.”

Schumer said that while Democrats oppose the wall money, they agree on other ways to secure the border “and that bodes well for coming to an eventual agreement.”

Trump is risking backlash from conservatives who pushed him to keep fighting for the wall. Some lashed out Friday for yielded, for now, on his signature campaign promise.

Within the White House, there was broad recognition among Trump’s aides that the shutdown pressure was growing and the standoff could not stretch on indefinitely. The president’s approval numbers had fallen during the impasse. Several Republicans were calling on him, openly and in private, to reopen the government.

The breakthrough came as LaGuardia Airport in New York and Newark Liberty International Airport in New Jersey both experienced at least 90-minute delays in takeoffs Friday because of the shutdown. And the world’s busiest airport — Hartsfield-Jackson Atlanta International Airport — was experiencing long security wait times, a warning sign the week before it expects 150,000 out-of-town visitors for the Super Bowl.