[dx87]

They are only allowed to contradict state laws to the extent that the federal government may decide it's not worth it to try and enforce the rules in the state, especially states like CA where they state that they won't cooperate with enforcement of laws they don't agree with. Even if the state someone lives in has contradictory laws, you still have to follow the federal laws at any job that cares about that. For example, if you live in a state that has legalized recreational or medical marijuana, you still can't use it if you want to work a federal job or anything that requires a security clearance.