A preemption is a total or partial federal assumption of power in a
particular field, restricting authority of states. A total preemption is federal government's assumption of all regulatory
powers in particular field. Partial preemption is state law on same subject is valid unless it collides with federal laws.
Standard partial preemption is states permitted to regulate activities regulated by federal government. Most of the United
State's federal preemptions rely on the National Supremacy Clause.