New York v. United States

This case addressed the constitutional principles of sovereignty and severability. The Tenth Amendment reserves for the states all powers not delegated to the federal government, but in the century preceding the New York decision, the Court had tended to favor the federal government in Tenth-Amendment cases. The New York ruling placed limitations on both federal and state power. Less obvious was the relevance of the case to severability or separability, which is the idea that the Court can invalidate certain portions of a statute but leave others intact.