
Quoting
divemedic
On the one hand, strict Constitutionalists (I am among those with those beliefs) believe that Congress's power should be limited to only those duties listed in the Constitution. All other powers should be vested to the people and the state governments. The Tenth Amendment specifically says, "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
On the other hand, more liberal interpreters of the constitution allow for powers more tangential to those duties. Many individuals cite the Necessary and Proper and the Commerce clause as grounds for their argument. The overall trend has seen more power shifting to the Federal Government generally, and specifically to Congress. ( A good example of this is to ask where the Government gets the power to 'bail out' companies or even provide free money to individuals. Heck, 90% of Federal Law uses those 2 clauses for justification.)