Command in Afghanistan is changing, but strategy is not. After nearly a decade of war, the goal of breaking the Taliban's momentum seems no closer. Yet on one point there remains near-consensus among policymakers. Since Afghanistan's drug trade contributes to the strength of the Taliban and the weakness of the government, fighting the drug traffic is agreed to be integral to fighting the insurgency.

Alas, this intuitively appealing idea is almost precisely the opposite of the truth. Yes, the drug trade helps the Taliban and harms the Afghan government. But efforts to fight drugs strengthen the insurgency rather than weaken it. Counter narcotics policies reward those who remain successful drug-dealers, concentrating those rewards in the hands of the Taliban, warlords and corrupt officials.

Anti-drug policies run into the law of unintended consequences and, more brutally, the laws of supply and demand. Afghanistan has a virtual lock on world opium production: it is both the incumbent and by far the lowest-cost supplier. Extensive inventories, estimated at two years' worldwide consumption, preclude shortages. Retail demand for the heroin produced from Afghan opium is only slightly sensitive to export prices, because most of its retail price consists of distributors' mark-ups rather than the raw material price.