In applying the Supremacy Clause to subjects which have been regulated by Congress, the primary task of the Court is to ascertain whether a challenged state law is compatible with the policy expressed in the federal statute. When Congress legislates with regard to a subject, the extent and nature of the legal consequences of the regulation are federal questions, the answers to which are to be derived from a consideration of the language and policy of the state. If Congress expressly provides for exclusive federal dominion or if it expressly provides for concurrent federal-state jurisdiction, the task of the Court is simplified, though, of course, there may still be doubtful areas in which interpretation will be necessary. Where Congress is silent, however, the Court must itself decide whether the effect of the federal legislation is to oust state jurisdiction.6
6 Treatment of preemption principles and standards is set out under the Commerce Clause, which is the greatest source of preemptive authority.
Last modified: September 7, 2012