MBE Rules · Constitutional Law
Preemption — express, field, conflict
The rule
Federal law preempts state law when Congress (1) expressly says so, (2) so pervasively regulates the field that Congress left no room for state regulation (field), OR (3) state law conflicts with federal law — impossible to comply with both (impossibility) or state law stands as obstacle to federal purpose (obstacle).
In plain English
Federal law can override state law if Congress clearly says it should, if federal rules cover an entire area, or if state law makes it hard to follow federal law.
Worked example
A state law allows a pesticide banned by federal law. The federal ban preempts the state law because it's impossible to follow both regulations.
Memory hook
Preemption: Express, Field, Conflict. Congress commands, covers completely, or clashes. Federal law rules when Congress says, when the field's full, or when there's friction.
The trap
Students think: Any federal law overrides state law. Wrong, because preemption requires express, field, or conflict. The actual test is whether Congress intended to preempt state law.
How examiners test it
The MBE loves: state law in area with federal regulation. Question: preempted? Trap: students miss express preemption clause or overlook federal field occupation.
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