President Claudia Sheinbaum shrugs as two CIA officers are killed in Chihuahua.

Deaths in Mexico’s modern cartel wars are nothing unusual: The sanguinary toll of nearly 20 years of bloodshed, of state vs. criminals vs. citizenry, exceeds that of most major wars. But American deaths in Mexico are unusual—especially deaths of Americans present in an official capacity.

That alone would make notable last weekend’s reported death of two Central Intelligence Agency officers in the Mexican state of Chihuahua. Those fallen Americans, killed in the line of duty against Mexico’s cartels, are a sign of a crisis in relations between the U.S. and Mexico.

It is a crisis created by Mexico’s regime, which has cooperated for too long with its own cartels and must now reap the predictable result as Americans act to protect themselves. When Americans crack down on cartels, they aren’t doing it only for American interests; they’re also protecting the Mexican majority that yearns for a defense against the cartels. These CIA officers—apparently killed in a car that crashed and then exploded—are said to have been accompanied by Chihuahuan officials, two of whom also died.

American and Mexican alike gave their lives in the fight against some of the worst people on earth in Mexico’s narco-terror cartels. But that isn’t how President Claudia Sheinbaum and her Morena party see it. Asked about the deaths, the Mexican president expressed ignorance of the cooperation between these CIA officers and local Chihuahuan authorities and indignation that American forces would operate on Mexican soil.

The profession of ignorance was at least in part performative. Ms. Sheinbaum and her security chief, Omar García Harfuch, have been quietly allowing expanded American operations in Mexico since Donald Trump returned to the White House. Americans provided intelligence in the killing of cartel leader Nemesio “El Mencho” Oseguera Cervantes on Feb. 22. Much more is happening off the record.

Nonetheless, the Mexican regime’s scapegoats are the Americans, who supposedly violated Mexican sovereignty, and the governor of Chihuahua, who supposedly invited them in. That governor, María Eugenia Campos Galván, who has been summoned to Mexico City to testify, is from the major opposition party.

The Trump administration has so far tolerated this double game. Ms. Sheinbaum and her party promote anti-American hostility in multiple venues—from material support for the Cuban dictatorship to condemnation of the Jan. 3 American raid on Caracas, routine social-media posts reminding Mexicans of historical U.S. injustices, and disparagement of Mr. Trump’s policies. Yet Ms. Sheibaum’s government has also participated in enhanced action against cartels, and closer operational—though not strategic—integration with the Americans. Implicit in all this is protection for the several million American citizens who live in Mexico, the largest community of U.S. expatriates, who have thus far mostly been spared cartel violence.

Mr. Trump is taking note of the Mexican president’s public callousness. Responding to secondhand reports of his displeasure with the Mexican response, White House press secretary Karoline Leavitt went on record stating that some sympathy from Mexico for the dead agents “would be well worth it,” especially given that they defended Mexicans as well as Americans. Ms. Leavitt is right. The Mexican government has presided over the disappearances of tens of thousands of Mexicans, sought to play down the discovery of a cartel extermination camp at Teuchitlán, and consistently shielded its own senior politicians known to collaborate with cartels.

Mexico’s government faces serious difficulties. The country’s economy is steadily deteriorating. The Trump administration’s aggressive focus on Western Hemisphere security has deprived Morena of its narco allies in Venezuela and Bolivia, and Cuba may join that list. Mexican officialdom is well aware that the Mexican economy is kept afloat by a combination of migrant remittances and North American market access. This is why, even as the president of Mexico has been cold about the American dead, Mexico’s bureaucracy warmly welcomed the U.S. trade representative this week.

The question for the U.S. is whether to tolerate the longstanding duplicity. Two Americans are dead in the honorable service of their country. Two Mexicans died with them, also honorably serving their country. America will see to its own security—and to Mexico’s too, if the Mexican government will allow it. If it won’t, then America will look to other friends to the south.