Five days into Donald Trump’s presidency, he signed an executive order to mandate the construction of a wall on the U.S.-Mexico border. He then gave an interview to ABC News saying Mexico would be paying for it. A day later, he tweeted that if Mexican President Enrique Peña Nieto was unwilling to do so, then the two leaders should not be meeting, as scheduled, on January 31st. Peña Nieto announced shortly thereafter that he was canceling the meeting, breaking with the longstanding tradition that incoming U.S. presidents meet with their counterparts from Mexico and Canada soon after assuming office.

Before President Trump finishes his first week in office, before even having a secretary of state in place, he has already managed to alienate a friendly neighbor, America’s third-largest trading partner and close ally. All this over an outrageous campaign promise.

Trump now faces a southern neighbor largely united in its anti-U.S. sentiment. This sentiment is not primarily moved by his intention to renegotiate NAFTA; or his racist, anti-Mexican rhetoric; or even by the idea of the wall itself, which anyone who has actually been to the U.S.-Mexico border knows is patently absurd given the topography along the 2,000-odd mile length of the border—not to mention the large swathes of protected or privately owned land there. The sentiment, which led every single political leader in Mexico to demand that President Peña Nieto cancel his trip to Washington, comes from the indignity of the notion that Mexico will somehow pay for the wall. The Trump administration is basing its entire approach to the bilateral relationship with Mexico on a ludicrous and arrogant proposition: that it can make another sovereign nation foot the bill for its own xenophobic construction project.

Trump has recklessly and needlessly ushered in a dark era in U.S.-Mexico relations. Gratuitously bashing Mexico and Mexican immigrants plays well with Trump’s base, and in his ignorance, he seems to believe he can do it without consequences. With the possible exception of Canada, there is no other country with as many areas and levels of cooperation with the U.S. as Mexico. Issues of trade, transportation, national security, organized crime, water, the environment, health, and immigration that affect both countries rely on extensive bilateral cooperation and goodwill.

As Mexico prepares for a presidential election in 2018, every candidate worth his or her salt will try to outdo the competitors in anti-U.S. posturing. They will promise to expel armed U.S. law-enforcement personnel from Mexico, to legalize drugs, to allow Central American migrants to reach the U.S. border, to stop sharing water with drought-ravaged border states. Some of them, if elected, may even want to emulate Trump and follow through on their most ridiculous campaign promises. The voters, for sure, will be egging them on to stick it to the United States.

From an early age, every Mexican is taught that Mexico lost half its territory to its imperialist northern neighbor. Ask any Mexican child and they will name all six “Niños Heroes,” young cadets who died defending Chapultepec castle from the invading U.S. forces in 1847. One of them is said to have wrapped himself in the Mexican flag and jumped to his death rather than be captured by the Americans. His story might be as apocryphal as George Washington's cherry tree, but it nonetheless remains a powerful symbol of Mexican nationalism: We will just as soon suffer hardship, or even death, than be submitted to humiliation from the U.S.

In his seminal book on U.S.-Mexico relations, Distant Neighbors, Alan Riding examined the Mexican presidency at the end of the 20th century. He described a system with a president so powerful he could do whatever he wanted, except for two things: run for reelection and bring the country closer to the United States. Decades after Riding's book was published, reelections are still not permitted at the presidential level, but successive presidents did manage to overcome historic and deep-seated suspicion of the U.S. to a point where most Mexicans viewed their powerful neighbor favorably and the two countries began to collaborate politically, economically, and culturally as never before.

When Trump attacks Mexico, when he blithely says that Mexico will pay for the wall, he is not pre-conditioning a negotiating counterpart. Instead, he is undoing years of patient diplomacy and riling up a long-dormant Mexican nationalism. He is telling us that our old suspicions were right and that the U.S. is a foe, a bully not to be trusted.

In essence, Trump is limiting the Mexican president’s range of negotiation, because any concession will now be seen as a sign of weakness, a loss of pride, an attack on our sovereignty. The result is Peña Nieto's cancellation of his Washington visit. Trump has instantly made an enemy out of a friend. As things stand now, the United States is not talking to a neighbor and trusted ally because of a campaign promise so preposterous nobody took it seriously.

Even if the situation is somewhat ironed out when the new State Department team is in place, even if both presidents meet and smile and agree to work together, the sentiments of nationalism and mistrust wrought by Trump will permeate throughout the bureaucracy and will be hard to eradicate. Expect less bilateral cooperation in the future, less information-sharing, and less goodwill, all because of Trump's wall. Mexico would just as soon suffer economic hardship than pay for something so stupid, so offensive, and so useless. If you don’t believe me, go to Mexico and see the monuments we erect to the Niños Heroes for giving up their lives resisting the U.S. invasion.