Incoming White House acting chief of staff Mick Mulvaney on Sunday acknowledged that the Department of Homeland Security can't force Mexico to pay for a wall along the southern border.

"Technically, you and I both know that it cannot work exactly like that. ... Department of Homeland Security can’t actually spend money from Mexico. We have to get it from Treasury," Mulvaney said during an interview on ABC's "This Week."

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President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE repeatedly pledged while campaigning for president that he would force Mexico to pay for a wall along the border.

Mulvaney also claimed Sunday, however, that Mexico would essentially pay for the wall through the new trade deal known as the United States-Mexico-Canada Agreement (USMCA).

"USMCA, which is so much better for us than the [North American Free Trade Agreement] deal that American workers are going to do better, the government is going to do better and you could make the argument that Mexico is paying for it in that fashion," he said.

The federal government entered a partial shutdown on Saturday after lawmakers could not agree to Trump's demand for $5 billion in funding for the wall.

The White House previously signaled that Trump would sign a bill that didn't include that funding, but the president reversed course late last week, leading to the shutdown.