"The fact is Mexico will pay for the wall. It was discussed that it wouldn't be discussed but they know my stance and I know their stance," he said. "And until I'm president, I'm not going to press anything very much but they fully know my stance. My stance is we're going to build a wall and Mexico's going to pay for the wall. It's very simple."
In August, Trump met with Peña Nieto in Mexico and attended a news conference alongside him. At the news conference, Trump said he and Peña Nieto had talked about his campaign promise to build a wall along the U.S.-Mexico border.
"We did discuss the wall. We did not discuss payment of the wall. That'll be for a later date," Trump said at that news conference Aug. 31.
Later that day, however, Peña Nieto took to Twitter, saying in two tweets written in Spanish that "at the beginning of the conversation with Donald Trump, I made it clear that Mexico will not pay for the wall."
Eduardo Sanchez, Peña Nieto's spokesman, also said that the Mexican president had started the meeting between the two by making a statement that included the direct declaration that his country would not be paying for the wall.
Earlier today, Hillary Clinton said that Trump did "choke."
"He didn't raise it, so he did choke. He didn't know how to even communicate effectively with a head of state. And I think that's a pretty clear outcome from that trip," she added, taking Trump's word that the issue was not discussed.
Trump today said Peña Nieto had not told him that Mexico would not pay for the wall.
"Oh, he didn't say that. He tweeted that long after the meeting was over," Trump said today. "The fact is that he didn't say that. He tweeted that after I left."
"I think we'll have a very good relationship," he said, "but Mexico will pay for the wall."
When asked whether the Mexican president had broken his word by talking about what they'd discussed, Trump said: "They all know the ground rules and the ground rules were there. ... We had ground rules and that's OK. They know my stance and I know their stance. See who wins in the end. We'll win 100 percent."
He continued: "They're going to pay for the wall. We're going to build a wall. They're going to pay for the wall. We're going to keep drugs out. ... We have all of these people flooding into our country. All of those people are going to get out. We're gonna get'em out."
ABC News' Candace Smith, Morgan Winsor and Meghan Keneally contributed to this story.