Republican presidential nominee Donald Trump has repeatedly called for Mexico to pay for a border wall – among other concessions – during his 2016 campaign. But that all changed when he actually visited Mexico. (Peter Stevenson/The Washington Post)

This post has been updated.

Over the past 14 months, Donald Trump has been telling anyone within shouting distance that he will not only build a big, beautiful border wall along the U.S.-Mexico border, but also that Mexico would somehow be made to pay for it.

It's among the most brazen claims he has made as a presidential candidate — the idea that a foreign country would fund the construction of a wall built mostly to protect the United States. And yet, Trump said that this did not come up during Trump's meeting Wednesday with Mexican President Enrique Peña Nieto.

Trump said that the small matter of who pays for his massive border wall — at an estimated cost of between $15 billion and $25 billion, per The Washington Post's Glenn Kessler — somehow wasn't mentioned during his meeting with the man whose government would be footing the bill.

Speaking after meeting with Mexican President Enrique Peña Nieto Aug. 31, Republican presidential nominee Donald Trump said they did not discuss the payment for the border wall that he has pledged to build and have Mexico pay for. (The Washington Post)

"We did discuss the wall," Trump said during a brief Q&A session. "We didn't discuss payment of the wall. That'll be for a later date. This was a very preliminary meeting." In what was otherwise a positively received visit — drawing praise even from some Trump critics such as Bill Kristol and former Hillary Clinton spokesman Howard Wolfson — it stuck out like a sore thumb.

There's just one catch: Peña Nieto tweeted out that the subject did come up -- and that he'd raised it.

It's not clear who's telling the truth here. Peña Nieto could have corrected Trump's comments during the Q&A, but didn't. But it makes sense (as we explain below) that he would have raised the subject, and Trump does have something of a reputation for contradicting other people's accounts of meetings he was in.

The wall holds a special place for Trump, even as he is clearly softening his stance on illegal immigration. The wall is not negotiable, and he has said Mexico will pay for it about as often as he has brought it up. It's a call-and-response line at his rallies — maybe his most iconic pledge.

Given the frequency with which he has used this line, the idea that he wouldn't bring it up when he is given the chance suggests a softness we haven't seen before.

Trump supporters will say that this meeting is merely the first step in a relationship between Trump and Mexico, just as Trump himself did.

Update: A Trump aide with knowledge of meeting indeed says, "Both parties knew each other’s positions going into today, and we didn’t think it was appropriate to start negotiating during this meeting."

But for a guy whose proposal to have Mexico pay for the wall has largely been dismissed as a ridiculous assertion, not bringing it up in a meeting with the Mexican president will only further that perception.

This wasn't the first time that Peña Nieto has said Mexico will not pay for the wall. "There is no way that Mexico can pay [for] a wall like that," he told Fareed Zakaria last month.

It was probably inevitable that Peña Nieto would raise the topic. The potential next U.S. president, who has labeled illegal immigrants from your country as "rapists" and "criminals," is in your country, and you have the chance to talk to him about anything. It's perhaps understandable that you wouldn't get into a back-and-forth over the "rapists" and "criminals" comment — keeping things cordial, after all — but Trump has been saying for more than a year that he is going to force you to pay for something very, very expensive that your citizens will probably not like having to pay for.

What's more, the method by which Trump has said he would force Mexico to pay for the wall — by preventing immigrants from sending billions of dollars home to Mexico — would have serious economic consequences. As Bob Woodward and Robert Costa reported:

The proposal would jeopardize a stream of cash that many economists say is vital for Mexico’s struggling economy. But the feasibility of Trump's plan is unclear both legally and politically, and it would test the bounds of a president’s executive powers in seeking to pressure another country.

In the memo, Trump said he would threaten to change a rule under the USA Patriot Act anti-terrorism law to cut off a portion of the funds sent to Mexico through money transfers, commonly known as remittances. The threat would be withdrawn if Mexico made “a one-time payment of $5-10 billion” to pay for the border wall, he wrote.

“It’s an easy decision for Mexico,” Trump said in the memo, on campaign stationery emblazoned with “TRUMP Make America Great Again!”

This is a serious economic threat with big-time consequences, should Trump become president. It made sense for Peña Nieto to reiterate where he stands on this and urge Trump to knock it off (in a diplomatic way, of course).

What's more, this was a moment of strength for Peña Nieto: Trump's immigration proposals have been wavering.

Trump will detail his latest immigration policy in a speech on domestic soil Wednesday night, and reporters will be watching like hawks for what he says about the wall.

There are two options: If he doesn't say Mexico will pay for it, it will look like another flip-flop — as though he is backing off that signature promise, too. If he does bring it up, it risks overshadowing whatever diplomatic progress he might have been made during this meeting — progress being credited to Trump.

Trump's over-the-top rhetoric, of course, is what put him in this position. He is being made to either deliver on a promise that could cause serious strain on diplomatic ties between the United States and a neighbor, or to look like a guy who talks a big game but can't close the deal.

And with the late accusation by Peña Nieto, Trump is looking like something even worse: A politician.


Update: The Clinton campaign's John Podesta sent out two responses to Trump's meeting, one before and one after Peña Nieto's statement that the wall had come up. The first one said that Trump "choked" by not raising the subject. The second, after the Mexican president weighed in, was even less generous: "It turns out Trump didn't just choke, he got beat in the room and lied about it."

Update: Peña Nieto's spokesperson explains the discrepancy.