President Donald Trump said he could declare a national emergency to circumvent Congress and build a wall along the U.S. border with Mexico, after telling Democrats he’s prepared to keep part of the government shut down for a year or longer if his demands aren’t met.

“Absolutely we can call a national emergency because of the security of our country,” Trump said Friday at the White House. “I haven’t done it. I may do it. We can call a national emergency and build it very quickly.”

“The president’s authority in this area is intended for wars and genuine national emergencies,” Evan Hollander, spokesman for the House Appropriations Committee, said in a statement. “Asserting this authority to build a wasteful wall is legally dubious and would invite a legal challenge from Congress.”

Trump made the comments moments after Democratic leaders left the White House saying there’d been no progress toward a deal during a nearly two-hour meeting. House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer said the meeting was contentious, and that Trump refused their proposal to reopen government and deal separately with the dispute over the wall.

Trump, however, said moments later that the meeting had been productive. The sides agreed to meet over the weekend, and Trump expressed optimism that an agreement could be forged. The president tweeted Saturday that there is “great support coming from all sides for Border Security on our very dangerous Southern Border.”

Trump continued to tweet about the wall on Saturday, terming the southern border “very dangerous” and claiming support from all sides for his position.

Trump’s Friday comments were met with skepticism within his own party and sharp criticism from Democrats. Several lawmakers and experts said Congress would still be required to allocate the funds for the wall even if the president declared a national emergency.

“He could declare an emergency, but that does not create the funding,” said former Republican Senate Budget Committee staff director Bill Hoagland. “Congress would still have to fund the emergency.”

Parts of the U.S. government are now into a 15th day of shutdown after Trump refused to sign a spending bill that didn’t include billions of dollars to continue construction of a border wall, his top campaign promise. He remains at an impasse with congressional Democrats, who consider the proposed wall a waste of money.

Douglas Holtz-Eakin, president of the American Action Forum and former director of the Congressional Budget Office, said Trump would still need Congress for the funds if he pursued the national emergency strategy.

Washington Democrat Adam Smith, incoming chairman of the House Armed Services Committee, said Trump would be harming the military if he tried to fund the wall through a national emergency declaration.

“Diverting money from these military construction accounts could have substantial impacts for service members at installations across the country and on defense projects that are important in supporting readiness, training, operations, and quality of life for military personnel and their families,” Smith said.