For roughly four decades, a clear foreign policy rule set has existed between the United States and Latin America, centering largely on the question of counternarcotics. Starting with Richard Nixon's "war on drugs," an explicit quid pro quo came into existence: U.S. foreign aid (both civilian and military) in exchange for aggressive Latin American efforts to curb both the production and trafficking of illegal narcotics (primarily marijuana and cocaine).
By virtually all accounts, that logistics-focused strategy has proven to be a massive failure. America's focus on interdiction and prohibition has not stemmed domestic drug abuse. Instead, all indications are that preventative education -- on a generational scale -- has proven far more effective, meaning that demand reduction has trumped supply curtailment as a means of reducing overall prevalence.
Meanwhile, across Latin America, there's been widespread movement toward decriminalization. Why? Because the benefits of remaining on America's "good side" on this hot-button issue have been overwhelmed by the negative externalities of overcrowded prisons, rampant drug-related violence, police corruption, and growing organized criminal networks.