Response on Virginia, the NDAA and the Supremacy Clause

I've gotten a number of interesting responses to my post from earlier today on Virginia's proposed law forbidding state cooperation with NDAA-related detention activity that might impact citizens. One correspondent, who prefers to remain nameless, writes in that:

You'd think that Virginia would have learned its lesson the last time it tried to nullify a federal law.  Its attempt to block Obamacare was laughed out of Court by the Fourth Circuit, which held that the state lacked standing to enforce it.

On the other hand, Columbia law professor Matthew Waxman wrote me to insist that there's more to Virginia's nose-thumbing legislation than my dismissive post allows:

It's a much more complicated issue than a straight supremacy clause matter, and as I discuss in my recent National Security Federalism article, there are many other instances of states and localities taking similar positions with respect to post-9/11 federal law.  True, very often these resolutions are mostly hortatory or symbolic because of the nature of the issue and the fact that the law is generally carried out by federal agents, but because the federal government sometimes requests voluntary assistance from state and local agencies, they could have practical effects.  Other similar examples include state and local laws regulating cooperation with federal agencies implementing USA PATRIOT Act provisions (detailed in a 2009 Yale Law Journal article by Jessica Bulman-Pozen and Heather Gerken).  Also, for example, see this editorial from yesterday by the Mayor of Portland, Oregon, about how local law binds local police agents' participation in FBI-led Joint Terrorism Task Force work.