In 2006, Mexico’s newly elected president, Felipe Calderón, declared war on his country’s drug cartels. He militarized and intensified a conflict that had been managed by his predecessors through an opaque strategy of accommodation, payoffs, assigned trafficking routes, and periodic takedowns of uncoöperative capos.

The “war” is going poorly. Mexico’s murder rate, which had fallen by fifty percent between 1992 and Calderón’s inauguration, has about tripled since then. A murky, multi-sided conflict has descended into one involving severed heads displayed on pikes, mass executions, disappearances, attacks on journalists, and urban shootouts among the cartels’ trained paramilitaries. About forty-five thousand Mexicans have died since Calderón called out the dogs. Many thousands of the victims are public servants—police, judges, mayors, and legislators—or civilians caught in crossfire. In the name of defending them, the country’s military has carried out horrifying atrocities, degrading the legitimacy of a state that was weak enough to begin with, as a Human Rights Watch report released this week documents.

For all this, the flow of marijuana, cocaine, heroin, and crystal meth into the United States—although hard to measure with any precision—has not been substantially reduced.

“Politicians are lost for language to even describe the conflict,” writes Ioan Grillo, an English-born journalist, in his new book, “El Narco: Inside Mexico’s Criminal Insurgency”:

Felipe Calderón dresses up in a military uniform and calls for no quarter on enemies who threaten the fatherland—then balks angrily at any notion Mexico is fighting an insurrection. The Obama administration is even more confused. Secretary of State Hillary Clinton assures people that Mexico is simply suffering from inner city crime like the United States in the eighties. Then she later says Mexico has an insurgency akin to Colombia’s…. Is it a “narco state”? Or a “captured state”? Or just in a right bloody state?

The Mexican public is understandably ambivalent; it wants violence reduced but not at the cost of empowering nihilist warlords. “Protesters march to condemn the abuses of soldiers; but they also protest how the government is failing to protect them from gangsters,” Grillo records. “Often these two points are protested in the same marches.”

Grillo’s book is terrific—full of vivid front-line reporting; diverse interviews; a sense of history; a touch of social science; clarifying statistics; and realistic reviews of what might be done to improve things, none of it easy. It is essential reading. (If you have not already, read, too, my New Yorker colleague William Finnegan’s great reporting from the front lines.)

America has established a role in Mexico’s drug conflict of a sort Graham Greene would recognize. We are deeply culpable, and yet have managed, so far, to insulate ourselves from the highest costs.

In 2010, the border metropolis of Ciudad Juárez had more than three thousand murders. El Paso, just across the Rio Grande, had five. Crack Texas policing and tighter border surveillance cannot explain the gap; informal cartel policy does. It is in the cartels’ interest to keep America’s drug users apathetic and Pentagon generals unprovoked. In Cancun, where hundreds of thousands of Americans alight annually as tourists and spring-breakers, the “war” is barely perceptible. What good is a terrified customer?

Relatively little American blood has been shed, but we supply guns and money to both sides. George W. Bush backed Calderón’s militarization with a $1.8 billion package of helicopters, police training, and intelligence coöperation. Obama has continued the program. Yet it is another American policy—our weak control of automatic weapons—that influences the war’s apocalyptic character more. The Bush Administration rolled back Clinton-era restrictions on high-powered rifles. States such as Arizona have loosened the sale of guns designed for war, not for hunting or self-defense. Between 2009 and April, 2010, more than sixty thousand firearms captured in Mexico were traced to U.S. gun stores, Grillo reports.

The Obama Administration has reportedly sent drones to help Mexico track cartel leaders and traffickers. If Mexico had America’s relative global military power, its own drones would probably be hovering over gun marts in suburban Phoenix and Tuscon, perhaps unleashing a few Hellfire missiles at the owners, under the same interpretations of international law that the United States now employs to justify cross-border drone strikes against Pakistan’s logistical “safe haven.”

Then there are the dollars. American drug consumers provide the market the cartels battle each other to serve, of course. Nobody knows how much cash is transferred each year from the United States to Mexico for purchases of imported marijuana, cocaine, and synthetic drugs, but some estimates run as high as $30 billion annually. Marijuana probably accounts for most of the sales. I was surprised, perusing the 2010 United Nations World Drug Report, to see what a stoner nation we are. Almost one out of five Americans is estimated to use pot annually, according to the U.N. That is more than four times the rate in Mexico. It is irrefutable that the Mexican drug cartels exist because American politics and policy have not adequately recognized domestic illegal drug use as a public health issue, rather only as a crime. If you smoke, it would be ethical to smoke your own.

It is common for opponents of militarized and law-enforcement approaches to illegal drug use to advocate “decriminalization” and “legalization” of marijuana and other drugs as a sweeping solution. Marijuana would be the easiest to manage through decriminalization and public-health approaches, and more than a dozen American states have started to try in scattershot ways. But what works for pot doesn’t work the same way for cocaine, heroin, or synthetics. There are serious health, social, and safety questions that cannot be wished away. Science, public policy, courts, and police simply have not had the time—or the political support—to establish through trial and error what the most balanced, sustainable approach would be. The New Yorker’s Michael Specter, examining the case of Portugal, has laid out the most thorough review I’ve seen of how a rational public-health policy, integrated with policing and a functioning justice system, can make progress.

I read Grillo’s “El Narco” because I was headed to Mexico City for a couple of days, as part of a group of journalists and think-tank types. Earlier this week, we met activists, writers, political scientists, and three early candidates in next year’s presidential election, which is scheduled for July; because of term limits, Calderón must step aside. His center-right Party of National Action is trailing dismally in the polls. A restoration to power of the Institutional Revolutionary Party, or P.R.I., the author of Mexico’s twentieth-century authoritarianism, looks likely. Here is one more possible consequence of the drug war, and of the sharp rise in insecurity felt by Mexican voters: “We face the Putin-ization of Mexico,” Denise Dresser, a political scientist in the capital, remarked.

Surely Mexico deserves the best aid America can offer to reduce violence against civilians and strengthen a truly democratic state. But it is also a perverse practice to help Mexican forces arm and train themselves to fight their own countrymen, when many of their opponents are armed with Kalashnikovs obtained in America because we lack the common sense to keep machine guns off the market. We send them human-rights lawyers, guns, and money. And, as Warren Zevon added in the song by that name, “I’m the innocent bystander.”

Photograph by Adriana Zehbrauskas/The New York Times.