The U.S. Constitution (Article I, Section 8, Clause 18) grants to Congress the power to enact laws to carry out the enumerated powers (Clauses 1-17) that are specifically assigned to the federal government.
This clause became the center of controversy from the nation's early days when Alexander Hamilton and Thomas Jefferson tangled over the constitutionality of a national bank. Their arguments, in one form or another, persist today:
The loose constructionists (the Hamiltonians or Federalists) viewed Clause 18 as an opportunity to increase federal power.
The strict constructionists (the Jeffersonians or Anti-Federalists) believed that Clause 18 limited federal power. In their opinion, Congress could legitimately exercise only specified functions (Clauses 1-17); to do otherwise would be a violation of the Tenth Amendment, which specified that those powers not delegated to the federal government are reserved to the states or the people.