Something strange is happening to Carlos Villalon's trousers. We're trekking through a drenching rainstorm in the Chapare region of central Bolivia—a waterlogged sliver of primeval jungles and chocolate rivers that spill over their banks each winter with terrifying predictability. Eight policemen from Bolivia's special antidrug squad, the Leopards, are leading the way through the rainforest. They're looking for a primitive laboratory, often no more than a pit dug into the earth, lined with plastic, and covered by a thatch roof, where narcotraficantes turn coca leaf into coca paste, the first step in making cocaine. Half an hour into the hike, we notice the weird phenomenon taking place below Villalon's waist.

"Holy shit!" cries Evan Abramson, a 29-year-old Long Island–born expat whom I've hired as a fixer. "Hey, Carlos, man, check out your pants!" Villalon, our 41-year-old Chilean photographer, looks down. His once-green cargo pants have turned white, and they're brimming over with soap suds. "What the fuck?" he exclaims, running his hands over the foaming mess.

He lets loose a torrent of Spanish obscenities, and the troops cackle in amusement. It seems that during a recent power failure at his home in Bogotá, Villalon's laundress never put the trousers through the rinse cycle, hanging them up to dry instead, with the detergent suffusing every fiber, then stashing them back in his closet. Now the heavy rain—which has soaked through our ponchos, fogged our glasses, ruined our notebooks, short-circuited our cameras, and dissolved our cigarettes into wet shreds of tobacco and disgusting brown-stained scraps of paper—is performing the rinse cycle for him.

"When I get back to Bogotá, I'm gonna fire that fucking washerwoman," he says.

We press on through a tangle of giant ferns, spine-covered palms with roots that divide like octopus tentacles high above the ground, and wild papaya trees. Fire ants attack every exposed bit of flesh, leaving red welts. The soldiers curse but plod on, repeatedly sniffing the air like bloodhounds for the telltale chemical smell of a "maceration pit"—where coca is stomped into liquefied mash and the alkaloid is separated with a mix of gasoline, lime, and sulfuric acid. On top of all the other unpleasantness, the Leopards have only one machete among them, which makes hacking through the jungle next to impossible. At one point we find ourselves caught in thick brush with no apparent way out.

Up strides Armando Azturicaga, the lean-faced, no-nonsense officer who commands this unit. He's trained with the Green Berets at the School of the Americas, in Fort Benning, Georgia, then in Washington, D.C., with the Drug Enforcement Administration. He stares at Carlos's frothing trousers with an air of contempt. "This is bullshit," he says. "Let's get moving."

Azturicaga has been running drug interdictions in the Chapare for the past year and a half, and if he seems impatient with the way things are going, it's understandable. For two decades, the U.S. and Bolivian governments have worked closely together on an antidrug program (this year the budget is $34 million) that combines aerial surveys, on-the-ground destruction of coca plantations, raids on labs, and arrests of cocaine smugglers. But since Evo Morales, an Aymara Indian and the charismatic leader of a coca growers' union, became Bolivia's president, in January 2006, the jungle has exploded with coca leaf. Morales, 48, proposed a law that would almost double legal coca growing, ostensibly to promote the leaf's traditional use in Andean culture. At the same time, he's permitted the raids on cocaine laboratories and drug traffickers to go on unabated.

It's a strange paradox: The Leopards are working harder than ever, bushwhacking through the jungle seven days a week, taking down coke labs almost every day. Last year, the Leopards discovered more than 4,070 crude drug labs in the Chapare, an area roughly the size of New Jersey, as compared to 2,619 in 2005. Meanwhile, the cocaleros, the growers, are planting more and more of the leaf, with the government's encouragement. "It just keeps growing," Azturicaga says. Villalon, Abramson, and I look at one another, and the absurdity of the whole situation seems to hit us at the same moment. How the hell do you fight a war against coca, we wonder, when the cocalero in chief is running the country?