As anyone who is involved in drug policy can tell you, Afghanistan wasn't really America's longest war. That shady honor belongs to the war on drugs, which has been waged at the state, local, and federal levels for well over a century, even before President Richard Nixon officially declared in 1971 that he was starting "an all-out offensive" on the "drug abuse" he called "America's public enemy number one." Yet it's obvious that the drug war is in fact winding down. In the 1990s, medical marijuana was legalized in various states. Now 16 states have legalized recreational marijuana, with more to come. [...]