"He came out saying one thing and the Mexican president contradicted him almost immediately," said Clinton, referring to Trump's claim that he did not discuss payment for the border wall, a centerpiece of his presidential campaign.
"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.
But after the joint press conference in Mexico City, Mexican President Enrique Peña Nieto tweeted that the topic of the wall led off their conversation and said that he was unambiguous regarding his country’s stance.
"At the beginning of the conversation with Donald Trump I made it clear that Mexico will not pay for the wall," wrote Peña Nieto in Spanish.
To catch more of David Muir's interview with Hillary Clinton and Tim Kaine, watch "Good Morning America" at 7 a.m. Tuesday and "World News Tonight" at 6:30 p.m.
Clinton called the short trip, which only lasted a few hours, "unfortunate." Her running mate, Sen. Tim Kaine, then chimed in, saying, "If you're gonna cave when you're with an ally, and Mexico's an ally, what are you gonna do when you're with an adversary?"
Kaine added that he finds it "impossible to believe" that funding for the wall was not discussed, characterizing it as a "rookie mistake" by the GOP nominee.
"You shouldn't leave the safety of America and our diplomacy in the hands of a rookie who, on his one visit with a foreign leader, has already created kind of an international embarrassment for us," said the Virginia senator.
Muir also asked Clinton whether she'll accept Peña Nieto's invitation to visit Mexico before Election Day in November, as Trump did. Clinton responded, "No."
"I'm going to continue to focus on what we're doing to create jobs here at home, what we're doing to make sure Americans have the best possible opportunities in the future," said the Democratic presidential nominee.
Following his visit to Mexico last Wednesday, Trump flew to Arizona for a highly publicized speech about his immigration reform policies and was direct in his own right about who he believed would be footing the bill.
"We will build a great wall along the southern border," said Trump. "And Mexico will pay for the wall."