States, or to diminish their autonomy in its
employment, would be, in fact to remove their reason for being, and so
the reason for the Federal System itself.

So while the power of Congress to regulate commerce among the States and
with foreign nations is in terms a single power, in the intention of the
framers it comprised two very different powers. In the field of foreign
relations, the National Government is completely sovereign, and the
power to regulate commerce with foreign nations is but a branch of this
sovereign power. The power to regulate commerce among the States is, on
the other hand, not a sovereign power except for purposes of commercial
advantage; in other respects it is confronted at every turn by the
police power of the States, and hence requires to be defined in relation
to the known and frequently reiterated objectives of that power.

Indeed, it was urged on the authority of Madison that the power to
regulate commerce among the States was not bestowed upon the National
Government "to be used for * * * positive purposes," but merely as "a
negative and preventive provision against injustice among the States
themselves." Madison IV, Letters and Other Writings, 15 (Philadelphia,
1865). Furthermore, it is a power which was designed for the _promotion_
and _advancement_ of commerce, not a power to strike commerce down in
order to advance other purposes and programs. Grant that the power to
regulate commerce among the States is the power to prohibit it at the
discretion of Congress, and you at once endow Congress with power which
it may use as a weapon to consolidate substantially all power in the
hands of the National Government.

Thus, if Congress may prohibit _ad libitum_ the carrying on of
interstate commerce, it may make deprivation of the right to engage in
interstate commerce in any of its phases, even the right to move from
one State to another, a sanction of ever-increasing efficacy for
whatever standards of conduct it may choose to lay down in any field of
human action; and since laws passed by Congress in pursuance of its
powers are generally supreme over conflicting State laws, these
standards would supersede the conflicting standards imposed under the
police powers of the States. Henceforth, in effect, the police power
would exist solely by "leave and license" of Congress--as "the power to
govern men and things" it would be at an end; and by the same token the
Federal System, which is the ou