The new marijuana federalism is here, but is it here to stay? In this Article, I address that question by way of two related points, a practical one and a technical one, and I ultimately argue that state regulation should have a bigger role in fixing the limits of federal constitutional power. The practical point is that the current regime of state marijuana legalization is unstable, and it is a miracle that it is working as well as it is. Because marijuana remains contraband at the federal level, businesses and lawmakers who invest in responsible legalization at the state level have no guarantee their investments are safe from the whims of federal law enforcement. Moreover, even if the federal drug laws are not actively enforced in thos...