Trump took to Twitter on Tuesday night to say he looks "very much forward" to meeting with the Mexican leader. Pena Nieto's office confirmed the meeting with its own tweet, saying the two men would meet privately.
The unexpected trip comes as Trump seeks to clarify his stand on illegal immigration, a contentious issue that has been a centerpiece of his Republican presidential campaign. Trump has long called for deporting people currently living in the U.S. illegally and building a wall along the country's border with Mexico.
I have accepted the invitation of President Enrique Pena Nieto, of Mexico, and look very much forward to meeting him tomorrow.— Donald J. Trump (@realDonaldTrump) August 31, 2016
But in meetings recently with Hispanic supporters, Trump has suggested he could be open to changing the hardline approach he outlined during the GOP primaries. After one such roundtable this month, his new campaign manager said Trump's stance on deportations was "to be determined."
In the days since, Trump and his staff have broadcast varied and conflicting messages, with Trump himself saying one day he might be open to "softening" his stance, and days later saying he might, in fact, be "hardening."
Pena Nieto has been sharply critical of Trump's original immigration policy, particularly the Republican's insistence that Mexico would pay for the border wall. In a March interview, Pena Nieto said that "there is no scenario" under which Mexico would do so.
"I'd meet with him," Trump said of Nieto. "Absolutely, I'd meet with him."
In the same interview, Pena Nieto compared Trump's language to that of dictators Adolf Hitler and Benito Mussolini, saying it had hurt U.S.-Mexico relations. Former Mexican Presidents Vicente Fox and Felipe Calderon have also alluded to Hitler in describing Trump.
New Jersey Gov. Chris Christie, a close Trump adviser, has been among those pushing Trump to make the trip to Mexico, according to a person familiar with their conversations who spoke on the condition of anonymity in order to discuss them publicly. Christie made his own successful trip to Mexico City in September 2014 and has a warm relationship with the Mexican president.
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Pena Nieto extended invitations to visit Mexico to both Trump and Democrat Hillary Clinton last week. The Washington Post first reported Tuesday that Trump was considering making the trip to Mexico.
Trump is scheduled to speak on immigration Wednesday evening in Phoenix. He was already out West on Tuesday for a campaign stop near Seattle, giving him enough time to jet to Mexico before the Wednesday speech.
Trump's short stop in Mexico marks his first campaign visit to a foreign country. The Republican has faced a torrent of criticism from Clinton, a former secretary of state, about his preparedness to lead on the world stage. Several Republican foreign policy experts have also warned that Trump is unprepared for the numerous international issues that land on a president's desk.
Clinton's campaign has urged voters to not "be fooled" by what it calls Trump's attempts to disguise his immigration policies.
"Donald Trump will be who he has always been: Donald Trump," the campaign said in an email Tuesday night.
ABC News and The Associated Press contributed to this report.
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