Acting White House Chief of Staff Mick Mulvaney speaking in the briefing room of the White House in Washington, US, March 16, 2017. Photo: REUTERS/Kevin Lamarque/File Photo.

The White House chief of staff said on Sunday that the US federal government shutdown, now entering its third week, could “drag on a lot longer.”

But Mick Mulvaney also raised the possibility of changing the construction materials used to build a barrier on the border with Mexico in order to reach a compromise between President Donald Trump and Democrats.

Mulvaney, in an interview with NBC‘s “Meet the Press,” said Trump was considering accepting funding to build a steel fence, despite his campaign promise that the wall be built of concrete.

“And 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, who is also the head of the Office of Management and Budget, said.

Mulvaney said negotiations between his staff and congressional Democrats were bogged down in technical requests after the two sides met on Saturday morning.

“I think this is going to drag on a lot longer. I think that’s, that’s by, by intention,” Mulvaney, who is serving as the top White House aide in an acting capacity, said.

Large chunks of the federal government shut down on Dec. 22 after lawmakers and the president hit an impasse over Trump’s demands to build a wall. Trump is demanding any funding to keep the federal government operational also include $5.6 billion to begin building a $23 billion wall along the US border with Mexico.

Democrats in control of the House of Representatives this week passed a bill to reopen the government without providing additional funding for the wall, and have insisted that reopening the government should not be contingent upon wall construction funds.

Mulvaney dismissed claims from other Republicans that political motivations were preventing Trump for compromising. Republican Senator Lindsey Graham said last week that Trump’s political base would abandon the president if he did not build a wall.

“The president is interested in resolving this issue,” Mulvaney said. “It’s why we’ve been meeting for two weeks. It’s why we met yesterday with the vice president and the team for several hours. It’s why the president met with the leadership teams three days ago for several hours.”