Article VI: The Supremacy Clause
The Constitution is the supreme law of the land. If a state law or constitution contradicts a constitutional federal law, state judges are required to uphold the federal law.
In our system of federalism, in order for a federal law to be constitutional, it must be an exercise of Congress’s powers enumerated in Article I, Section 8. The Tenth Amendment specifies that powers not delegated to the federal government are reserved to the states and the people.
Supreme Court Chief Justice John Marshall cited the Supremacy Clause in cases that solidified federal power including McCullough v. Maryland (1819), and Gibbons v. Ogden (1824).