On October 1, 2009, Montana passed the Montana Firearms Freedom Act, the purpose of which was to regulate guns manufactured and kept within Montana state lines under a less restrictive regulatory regime than federal law provides. That same day, to ensure that Montanans could enjoy the benefits of this less restrictive state regulation, the Montana Shooting Sports Association filed a declaratory judgment claim in federal court. The lawsuit’s importance is not limited to Montana, as seven other states have passed laws similar to the MFFA and 20 states have introduced such legislation. The goal here is to reinforce state regulatory authority over commerce that is by definition intrastate, to take back some of the ground occupied by modern Commerce Clause jurisprudence. The district court granted the government’s motion to dismiss, however, and MSSA appealed to the Ninth Circuit. Now on appeal, Cato has joined the Goldwater Institute to file an amicus brief supporting the MSSA and arguing that federal power does not preempt Montana’s ability to exercise its sovereign police powers to facilitate the exercise of individual rights protected by the Second and Ninth Amendments. More specifically, for federal law to trump the MFFA, the government must claim that the Commerce and Necessary and Proper Clauses give it the power to regulate wholly intrastate manufacture, sale, and possession of guns, which MSSA argues is a state‐specific market distinct from any related national one. Our brief argues that federal preemption would violate the “letter and spirit of the Constitution” and that heightened judicial scrutiny is required whenever the federal government invokes an implied power to override state sovereignty. The MFFA should not be preempted because: (1) principles of state sovereignty limit federal power; (2) preemption would violate the federalism framework established in National League of Cities v. Usery; and (3) preemption would not allow state sovereignty to serve its role as a proper check of federal power. The Supreme Court has made clear that Congress is not the sole venue for states and individuals to seek protection from federal overreach and so this case is fundamentally a dispute over federalism — which should allow for state regulation of local matters to flourish in concert with federal power over “truly national” concerns. Allowing preemption here would have the perverse effect of allowing the federal government to regulate “states as states” while impairing states’ ability to operate in areas of traditional governmental functions. The Ninth Circuit should thus find that district court committed reversible error in dismissing the lawsuit and, as a result, MSSA should be allowed to pursue its case beyond the pleadings stage.