Marijuana Federalism: Uncle Sam and Mary Jane

On marijuana, there is no mutual federal-state policy; will this cause federalism to go up in smoke?
More than one-half the 50 states have legalized the use of marijuana at least for medical purposes, and about a dozen of those states have gone further, legalizing it for recreational use. Either step would have been almost inconceivable just a couple decades ago. But marijuana remains an illegal “controlled substance” under a 1970 federal law, so those who sell or grow it could still face fe...