I’m not sure what I think about that, Jonah. If a state or locality imposed trade barriers on other places, that would clearly be an interference with national commerce that the Congress would be right to invalidate. Couldn’t competitive subsidization reach the point where the subsidies functioned as reverse tariffs? One wouldn’t want to take this notion too far, either: You wouldn’t want Congress to keep states from competing via general tax reductions (although, to some extent, it already does).