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.