Republican candidate Donald Trump’s visit to Mexico was a textbook case of amateurish diplomacy, but there is something much more troublesome about it. It may resurrect Mexico’s anti-American revolutionary nationalism and hurt the United States for years to come.

Trump made a mess out of his Aug. 31 visit to Mexico. He first lavished praise on Mexican President Enrique Peña Nieto during their joint appearance in Mexico City — despite having vowed for the past 12 months that he would talk tough to the Mexican president — only to flip-flop a few hours later and deliver a fiery anti-Mexican speech in Arizona.

To make things worse, he claimed on that same day that he had not discussed with Peña Nieto who would pay for his proposed wall along the Mexican border. The Mexican president wrote later in a Twitter message that he had told Trump unequivocally that Mexico would not pay for the wall, in essence calling Trump a liar.

But the biggest fallout of Trump’s visit was an avalanche of criticism against Peña Nieto in Mexico for having invited Trump. Mexicans say Peña Nieto gave Trump a much-needed photo opportunity to look “presidential” on a podium alongside a foreign leader, and that he allowed Mexico to be humiliated by Trump’s anti-Mexican speech in Arizona immediately after he left Mexico City.

Peña Nieto was also lambasted for not having demanded an apology from Trump for having called Mexicans “criminals” and “rapists.” Trump is probably the most hated figure in Mexico. Only 2 percent of Mexicans have a favorable opinion of him, according to a recent poll by the daily El Financiero.

And Peña Nieto, whose popularity had already fallen to 25 percent before Trump’s visit, is now one of the most unpopular Mexican presidents in recent history. There is a massive anti-government march planned for Sept. 15, and several well-known columnists are asking for the president’s resignation.

“I don’t remember a president who is as weak, and so early in his term, as Enrique Peña Nieto,” said well-known writer Hector Aguilar Camín in the daily Milenio newspaper.

A big question now is how widespread, and how anti-American, Mexico’s growing nationalist reaction will be.

Mexico’ leftist populist opposition candidate for the 2018 elections, Andres Manuel Lopez Obrador, is already telling his cheering audiences that, if he wins, Mexico will no longer be a U.S. “colony” — much like what the Venezuelan and Cuban regimes tell their people every day.

Eduardo R. Huchim, a columnist with the daily Reforma, suggested that Peña Nieto could tell Trump that, if he wins, Mexico “will end its anti-drug cooperation” and “immediately revise the state of U.S. investments and transactions in this country.”

Peña Nieto “has unleashed a wave of nationalist fervor” in Mexico, wrote political scientist Jose Antonio Aguilar Rivera in Nexos magazine. He added that “the symbolic implications” of Trump’s visit with its “images of surrender, of blindness, are enormous.”

My opinion: Trump’s irresponsible diplomacy and cheap demagoguery against Mexicans, Muslims and others threatens to unleash a worldwide wave of anti-Americanism. He would be the perfect president for those who claim that the United States is a racist empire, and who use anti-Americanism as a tool to win popular support.

Mexico has a long history of anti-Americanism, which only subsided following the 1994 North American Free Trade Agreement. Generations of Mexicans have grown up with school textbooks that referred to Texas and California as “territories usurped from Mexico by the United States” in the 1830s and 1840s.

This is no trivial matter. If Mexico cut its anti-drug and anti-terrorist cooperation with Washington, U.S. drug trafficking and security problems in the United States would skyrocket overnight. And if Mexico strained bilateral ties, the United States could lose up to $108 billion in investments in Mexico and $584 billion in two-way trade that, according to a Wilson Center study, supports six million U.S. jobs.

With his visit to Mexico, Trump showed that he is not only a lightweight demagogue who can’t make a foreign visit without creating an international incident, but also that he would be a threat to U.S. national security who could unleash an anti-American nationalist backlash right next door.

— Andres Oppenheimer is a columnist for the Miami Herald.