The power of the federal government to prevent states from passing conflicting laws, and sometimes to prohibit states from passing any laws on a subject, is called what?

• A. Preemption
• B. Supremacy
• C. Reserved powers
• D. Enumerated powers

Answer: (A)

Preemption is the doctrine that federal law takes precedence over state law. Under the Supremacy Clause, when a federal statute conflicts with a state rule, federal law displaces the state rule, and in some cases can prohibit states from enacting any law on that subject. This is exactly the situation described: the federal government can prevent states from passing conflicting laws, or even bar state legislation on the topic altogether. The other terms describe related ideas but not the mechanism. Supremacy refers to the broader principle that federal law is above state law, reserved powers describe what states retain, and enumerated powers describe the specific powers granted to the federal government.