You could say the wall has been the centerpiece of Trump's presidential campaign.

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So when the GOP candidate flew to Mexico on Wednesday to visit with President Enrique Peña Nieto, many were curious whether Trump's plan for a wall along the U.S.-Mexico border would come up.

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"We did discuss the wall. We didn't discuss payment of the wall. That'll be for a later date," Trump said during a press conference following the meeting.

>> Full transcript: Here's what Donald Trump said about his immigration policy

Peña Nieto took to Twitter to disagree, writing, "At the beginning of the conversation with Donald Trump, I made it clear Mexico will not pay for the wall."

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>> Trump has made one thing clear: He's not softening on immigration

"And Mexico will pay for the wall. They don't know it yet, but they're gonna pay for the wall," Trump said later that evening at a campaign rally back in the U.S.