The state could probably get away with refusing to support the Feds, but not actively resist the law. Right now, the ATF, FBI, etc., all rely on some type of working relationship with sheriffs, state, and local police. If a county sheriff were to tell his deputies not to assist on raids or arrests, there's not much any Federal agency can do, as long as there's no active resistance. However, the cooperation, or lack thereof, works both ways. The local law enforcement has access to all kinds of Federal data from the FBI, ATF, etc. What happens if the Feds turn off those taps?
However, the Feds do have the power of the commerce clause, and the courts have already established Federal primacy when it comes to gun manufacturing. It'd be an uphill fight to counter that.