EveryCRSReport.com: Federal Preemption: A Legal Primer July 23, 2019 R45825 – “The Constitution’s Supremacy Clause provides that federal law is “the supreme Law of the Land” notwithstanding any state law to the contrary. This language is the foundation for the doctrine of federal preemption, according to which federal law supersedes conflicting state laws. The Supreme Court has identified two general ways in which federal law can preempt state law. First, federal law can expressly preempt state law when a federal statute or regulation contains explicit preemptive language. Second, federal law can impliedly preempt state law when Congress’s preemptive intent is implicit in the relevant federal law’s structure and purpose.

This report begins with an overview of certain general preemption principles. In both express and implied preemption cases, the Supreme Court has made clear that Congress’s purpose is the “ultimate touchstone” of its statutory analysis. The Court’s analysis of Congress’s purpose has at times been informed by a canon of statutory construction known as the “presumption against preemption,” which instructs that federal law should not be read as preempting state law “unless that was the clear and manifest purpose of Congress.” However, the Court has recently applied the presumption somewhat inconsistently, raising questions about its current scope and effect. Moreover, in 2016, the Court held that the presumption no longer applies in express preemption cases…”