Question

What is an exception to the general rule that if something is against the law on a federal level a state cannot decide it's legal arson of a federal building treasonous Acts or dumping of toxic waste

Answer 1

Short answer: The Supremacy Clause means a state cannot override a conflicting federal law, but there are important limits and exceptions: where federal law does not preempt the field, where state and federal governments have concurrent jurisdiction, and in practice when the federal government chooses not to enforce its law.

Key points, with examples:

- Supremacy Clause (general rule): If a state law actually conflicts with a federal statute or if Congress intended to occupy a regulatory field, the federal law wins and the state law is preempted.

- Concurrent jurisdiction / dual sovereignty: Many crimes are prosecutable by both state and federal authorities. That means a state can prosecute someone under state law even if the federal government could also prosecute the same conduct (and vice versa). It does not mean a state can “legalize” conduct the federal government punishes — it just means both sovereigns can bring charges. Example: someone who burns a building could face state arson charges and federal charges if the building is a federal facility.

- No preemption where Congress hasn’t occupied the field: If Congress didn’t intend to fully displace state law, states may regulate differently. Real-world example: many states have legalized marijuana even though it remains illegal under federal law (Controlled Substances Act). That state legalization does not nullify federal law; it just means states generally won’t prosecute under state law and federal authorities retain the power to enforce federal law.

- Federal enclaves/federal property: Acts that occur on federal land or against federal functions (e.g., treason, crimes on federal property) are generally federal matters. States have limited authority over federal enclaves, so a state cannot make arson on a federal building lawful insofar as federal jurisdiction applies.

- Practical non-enforcement: The federal government can choose not to enforce a law (policy decisions, resource priorities), which can make state legalization effectively tolerated, but that’s an enforcement choice, not a legal override.

So there isn’t a single “exception” that lets a state declare federally prohibited conduct lawful. The real exceptions are (1) where Congress left room for state regulation, (2) where the federal government chooses not to enforce, and (3) the fact that state and federal prosecutions can coexist under the dual-sovereignty doctrine.