Josh is the author of the critically acclaimed Unprecedented: The Constitutional Challenge to Obamacare (2013) and Unraveled: Obamacare, Religious Liberty, and Executive Power (Cambridge University Press, 2016). He states that “the supremacy clause does not prohibit states from legalizing controlled substances. A state is well within its own power to have a law on the books legalizing marijuana, not expend its own resources to criminalize marijuana, and hope the federal government doesn’t waste its time doing the same.” http://joshblackman.com/blog/2016/08/17/the-supremacy-clause-does-not-prohibit-states-from-legalizing-controlled-substances/