Federalism refers to the integration of a general government and small regional governments in a whole single political system.
There is a major difference between the Supreme Court’s reviewing the constitutionality of an act of Congress and the Court’s reviewing the states’ interpretations of federal law.
Under the supremacy clause, there is little doubt that federal law trumps inconsistent state law.
The Court’s power to review state court decisions about federal law was settled in 1816 in Martin v. Hunters Lessee (14 U.S. 304). In that case, the Court interpreted and applied a treaty of 1783 that protected Lord Fairfax’s claim to certain pieces of land in Virginia.
In McCulloch v. Maryland, the Court faced the dual challenge of assessing national legislation under the standard of Marbury and of declaring conflicting state legislation unconstitutional.