What is an exception to the general rule that if something is against the law on a federal level, a state cannot decide it is legal?

Question

arson of federal building
marijuana legalization
treasonous acts
dumping of toxic waste

Answer 1

An exception to the general rule that if something is against the law on a federal level, a state cannot decide it is legal is the legalization of marijuana. While marijuana remains illegal under federal law, several states have chosen to legalize it for medical or recreational use within their jurisdiction. This creates a conflict where the state's law contradicts the federal law on this particular issue.