Doctrine of Implied Powers- the Fed govt. may validly exercise power that is ancillary to one of the powers explicitly listed in the Constitution, so long as this ancillary power does not conflict with specific Constitutional prohibitions.
–    This notion of implied powers is itself explicitly stated in the necessary and proper  clause of Art I of 8: Congress may “make all Laws which shall be necessary and proper for carrying into Execution” the specific legislative powers by Art I. of 8, or by other parts of the Constitution.
–    So long as the means is rationally related to a constitutionally-specific object, the means is also constitutional (assuming that it does not violate any specific prohibition, such as those from the Bill of Rights).
–    Modern Import: The courts will not strike down a congressional action so long as Congress has employed a means which is not prohibited by the Constitution and which is rationally related to objectives that are themselves within constitutionally-enumerated powers.