The Supremacy Clause is an article of the U.S. Constitution that establishes that both the federal constitution and federal laws have precedence over state laws and constitutions, according to the Legal Information Institution of Cornell University Law School. It is found in Article 7, section 2 of the Constitution.
According to the Bill of Rights Institute, the Supremacy Clause was cited by two important cases that solidified federal power: McCulloch v. Maryland and Gibbons v. Ogden. According to The Free Dictionary, in McCulloch, the Supreme Court, led by Chief Justice John Marshall, invalidated a Maryland law taxing all banks in the state, including a Baltimore branch of the national bank. After finding constitutional authorization for a national bank, Marshall's opinion concluded based on the Supremacy Clause that "the government of the Union, though limited in its power, is supreme within its sphere of action."
Justia.com notes that in McCulloch and Gibbons, the latter of which held that even state government acts explicitly authorized by a state constitution are null when conflicting with federal authority, Marshall developed the full significance of the Supremacy Clause when he "gave the principle a vitality which survived a century of vacillation under the doctrine of dual federalism."