Mexican president fires back at Donald Trump: "Mexico will never pay for a wall"

Mexican President Enrique Peña Nieto lashed out at Republican presidential nominee Donald Trump after the two men met Wednesday in Mexico City, telling Trump that his country will not pay for a border wall between the United States and Mexico. 

"I repeat what I told you personally, Mr. Trump: Mexico will never pay for a wall," Peña Nieto tweeted. 

Peña Nieto's tweet Thursday afternoon was in response to a Trump tweet earlier Thursday morning, in which Trump merely said, "Mexico will pay for the wall!"

On Wednesday, Peña Nieto disputed Trump's claim that the two men never spoke about funding for the border wall that's become a central pillar of Trump's candidacy.

Trump told reporters at a news conference that the discussion of who would pay for the wall never came up. 

But Peña Nieto later said he explicitly told Trump Mexico would not pay for the wall. 

The continued brouhaha over the wall conversation now further squashes any goodwill Trump had built for his campaign following the meeting. 

Immediately following the meeting, even Trump critics conceded that Trump had pulled off his first attempt at foreign diplomacy. 

Yet Trump's apparent lie about the discussion over the border wall has turned the meeting into a mess that gives Hillary Clinton fodder for her claim that Trump is unfit for the world stage.

Clinton has made the argument that Trump is temperamentally unfit to be president a theme of her campaign — one she is unlikely to ditch for the final two months of the race.