WASHINGTON – "I will build a great, great wall on our southern border. And I will have Mexico pay for that wall," President Donald Trump said on June 16, 2015, when he announced his White House run.

"Mark my words," he said.

Americans did mark – and many mocked – those words, which Trump repeated at virtually every campaign stop after that announcement, up through the general election. But he is now arguing that he never said Mexico would pay for the wall directly.

"When during the campaign, I would say Mexico is going to pay for it, obviously I never said this. I never meant they're going to write out a check," Trump told reporters at the White House Thursday before departing for a review of the situation at the U.S.-Mexico border in Texas.

The U.S. is now locked in a 20-day partial government shutdown – poised to become the longest in American history – over Trump's demand that American, not Mexican, taxpayers fund the construction of a border barrier. Congressional Democrats have repeatedly pointed to Trump's past promises of Mexican payment in their refusal to grant his request.

"I said they're going to pay for it. They are," Trump said Thursday. He explained that Mexico would pay for the wall, which he now says will be a steel barrier, through the reduced trade deficit he believes will result from his renegotiation of the North American Free Trade Agreement.

The new deal, which the White House calls the United States-Mexico-Canada Agreement, or USMCA, has not yet been approved by Congress. Trump worried congressional Democrats might try to block the deal "because they want to do as much harm as they can."

"Obviously" he did not mean Mexico would cut the U.S. a check when he pledged "Mexico will pay for the wall, in front of thousands and thousands of people," he said.

"But they are paying for the wall indirectly many, many times over by the really great trade deal we just made," Trump said.

There are two major problems with Trump's assertions, however.

He did say Mexico would pay directly

During the campaign, Trump was generally vague about how Mexico would pay for the wall, saying, "They will pay in one form or another." But he also floated a number of specific ideas about how Mexico would pay for it.

An August 2015 campaign position paper said "Mexico must pay for the wall and, until they do," the U.S. would "impound all remittance payments derived from illegal wages," increase fees on visas and ports of entry into the U.S., and possibly implement tariffs or cut aid.

An April 2016 campaign memo outlined similar ways of pressuring Mexico. That plan explicitly said Mexico would make "a one-time payment of $5 - 10 billion" for the wall.

The memo also proposed threatening to block remittances from Mexican nationals in the U.S. back to Mexico – which the campaign said amounted to $24 billion a year. The plan was to then "tell Mexico that if the Mexican government will contribute the funds needed to the United States to pay for the wall," the rule blocking the money transfers would not be enacted.

"We have the leverage so Mexico will back down," the memo said.

A little more than two weeks before his inauguration, Trump admitted, in response to news reports, that taxpayers might have to initially pay for the "Great Wall (for sake of speed)" but vowed it "will be paid back by Mexico later!"

On Aug. 28, 2017, Trump told reporters at the White House that "it may be through reimbursement, but one way or another, Mexico will pay for the wall."

Trade deal won't pay for wall

A year ago, Trump told The Wall Street Journal that Mexico would pay for the wall "indirectly through NAFTA. OK?"

"You know, we make a good deal on NAFTA, say I’m going to take a small percentage of that money and it’s going to go toward the wall. Guess what? Mexico’s paying," Trump said.

Last month, Trump tweeted, "Our new deal with Mexico (and Canada), the USMCA, is so much better than the old, very costly & anti-USA NAFTA deal, that just by the money we save, MEXICO IS PAYING FOR THE WALL!"

But economic and trade experts told FactCheck.org that Mexico paying for the wall through the USMCA was "not possible."

In addition to the fact that all three nations still have yet to ratify the agreement, the money doesn't add up and the entire concept is based on a misguided perception of how trade works, experts said.

"USMCA is definitely positive for the U.S. economy but a fairly minor update to NAFTA," Kent Smetters, an economics professor at the University of Pennsylvania’s Wharton School, told FactCheck. "In fact, the additional revenue to U.S. relative to NAFTA would, optimistically, not cover annual maintenance and improvements of the wall much less the original build."

"In economic terms, the new deal is not, in fact, better than the old one, but it may (only may) benefit U.S. workers to a small extent," University of Michigan international economics professor Alan Deardorff said. "I don’t see any way that it actually brings in money to our government."

"Even if we accept conceptually the argument that government revenue attributable to the revised trade agreement constitutes ‘Mexico paying for the wall,’ there are no plausible assumptions of USMCA’s impact that would see government revenue increase by $25 billion," said Brookings Institution fellow Geoffrey Gertz, citing estimates for the cost of a concrete border wall.

Gertz also said Trump uses "a zero-sum view of trade, where one country’s gains are another’s losses – which cuts against the typical economists’ arguments that free trade is positive sum, that both sides to the agreement benefit."