From the Document: "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."
CRS Report for Congress, R45825
Congressional Research Service: https://crsreports.congress.gov/