Federal Law always trumps state law - always. Ask all the people who've been busted by the DEA for medical pot while following state and local law. The most recent attempts at Congress has given us a federal exemption for state laws regarding gay marriage, but they've passed other laws that more than likely unconstitutional when they get to the Court, it just takes years and years to make it that far, if the cowards will hear it. But sooner or later they are going to have to, and its going to be on this exact issue. Some state, say Kansas will deny the actions of NH or Mass. and those states will turn around and say "Well we no longer recognize the authority of Kansas to issue DLs, or corporate charters. But the current Congress could not even figure a way to keep habeas corpus around, so I don't have much hope in them