Can Congress issue legislation that preempts a state law that has already been passed?

In other words, if Congress were to pass legislation that preempted states from passing immigration reform like Arizona did in SB 1070, would that preemption also apply to the Arizona bill that had already been passed? Or does preemption only relate to future state legislation?|||They surely can. Federal law always preempts state law retroactively or otherwise. In the Arizona case, however, it looks like this will be decided in the courts. I imagine Congress would be very wary about passing legislation to nullify this law.|||Federal law always overrides a state law.|||Yes, Congress can preempt state law, whether state law has already been passed or will be passed.





Your referral to the Arizona bill is a non-sequitur, though. The Arizona law is merely a recitation of the federal law, which most states and the federal government don't enforce through fear of the extremely loud Hispanic lobby.|||The only way they could do that is to amend the Constitution.





If Arizona is the cause for allowing this current Congress to write any Amendment to the Constitution--we should just give them back to Mexico and be done with it.|||Yes they can. However, those that say federal law always supersedes state law are wrong. And if a federal law is in conflict with an already established state law, then the states can challenge the federal law or they can bring their grievances up with the US Attorney General.





It's untrue that federal is always above state law, since the states coexist along with the national government as semi autonomous sovereign states. States do have delegated powers and rights granted to them in the US Constitution; although, these days it isn't paid much attention to.