Legislative flexibility on the part of Congress will be the touchstone of federalism when the capacity to support combustion becomes the acid test of a fire extinguisher. Congressional flexibility is desirable, of course - but only within the bounds of federal power established by the Constitution. Beyond those bounds (the theory of our Constitution goes), it is a menace.

College Savings Bank v. Florida Prepaid Postsecondary Ed. Expense Bd., 527 U.S. 666 (1999)