On Nov. 2, Californians will vote on Proposition 19, deciding whether to legalize the production, sale and consumption of marijuana. If the initiative passes, it won't just be momentous for California; it may, at long last, offer Mexico the promise of an exit from our costly war on drugs. The costs of that war have long since reached intolerable levels: more than 28,000 of our fellow citizens dead since late 2006; expenditures well above $10 billion; terrible damage to Mexico's image abroad; human rights violations by government security forces; and ever more crime.