Unless Specifically Enabled it May Not Act

"I consider the foundation of the Constitution as laid on this ground that 'all powers not delegated to the United States, by the Constitution, nor prohibited by it to the states, are reserved to the states or to the people.' To take a single step beyond the boundaries thus specially drawn around the powers of Congress, is to take possession of a boundless field of power, no longer susceptible of any definition."

-- Thomas Jefferson (Opinion on the Constitutionality of a National Bank, 15 February 1791)