President Donald Trump on Thursday admitted that Mexico would not directly pay for the construction of his proposed wall along the southern border. Instead, he claims the wall will be paid for by revenue gained from a new trade deal pending in Congress.

"During the campaign, I said Mexico would pay for it," Trump told reporters outside the White House. "They are paying for it with the incredible deal we made, the USMCA."

That deal, short for the U.S.-Mexico-Canada Agreement, was approved by those three nations following lengthy negotiations over a replacement for the North American Free Trade Agreement, which Trump has long slammed as the "single worst deal ever approved."

The Trump administration has provided scant detail about how the USMCA would lead Mexico to pay for the wall, or if the increased revenue from the NAFTA replacement would actually reimburse the U.S. taxpayers who would directly fund the wall's construction.

The president, whose central campaign promise was that Mexico would pay for a wall stretching across the roughly 2,000-mile border, added: "When I said Mexico would pay for the wall in front of thousands and thousands of people ... obviously I never meant Mexico would write a check."

But on the campaign trail, Trump appeared to make that argument. A March 2016 memo to Washington Post reporters explained multiple ways to "compel Mexico" to "make a one-time payment of $5-10 billion" to keep the U.S. from cutting off the spigot of money it already sends to Mexico annually.

Sporting a white "Make America Great Again" cap, Trump made the remarks Thursday morning before boarding Air Force One to visit a Texas town near the border — his latest move amid fraying negotiations with Democrats over an ongoing partial government shutdown.

Once in Texas, Trump insisted again that, "When I say Mexico's going to pay for the wall, that's what I mean."

"I didn't mean, 'Please write me a check.' I mean very simply, they're paying for it in the trade deal," he added.

A day earlier, Trump walked out of a meeting with House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer after the Democrats said they would not approve funding for a border wall even if other parts of the government were opened up.

"I asked what is going to happen in 30 days if I quickly open things up, are you going to approve Border Security which includes a Wall or Steel Barrier? Nancy said, NO," Trump explained in a tweet as Pelosi and Schumer described the walk-out to reporters.

"I said bye-bye, nothing else works!" Trump added.

Schumer described Trump's behavior as a "temper tantrum," which Trump denied in a tweet Thursday morning.

Trump tweet cryin chuck

Trump is committed to his demand that any spending deal to fund nine federal agencies must include $5.7 billion to go toward a border wall. A letter from Trump's administration to Congress estimated, however, that that amount would only construct about 243 miles of a border barrier.

Democratic leaders, on the other hand, are refusing to provide any money toward a wall, and have suggested reopening as much of the government as possible while the deadlocked border security negotiations continue.