reated is to lay down the conditions on
which a designated branch of commerce among the States may be carried
on; that of the acts now to be treated is to eliminate outright a
designated branch of trade among the States. In other words, whereas the
former acts were, in general, preservative of the commerce which they
regulated because of its value to society, the latter regard the
commerce which they reach as detrimental to society. The third, and most
important difference from the point of view of Constitutional Law, is
the difference in relation of the two categories of acts respectively to
the reserved powers of the States. The enactments of Congress already
dealt with frequently intrude upon the ordinary field of jurisdiction of
the States; but when they do so, it is because the acts or things which
they thus bring under national control are regarded as "local incidents"
of interstate commerce itself. The relation of the enactments about to
be considered to the reserved powers of the States is precisely the
inverse of this. Their very purpose is to reach and control matters
ordinarily governed by the State's police power, sometimes in order to
make State policy more effective, sometimes in order to supply a
corrective to it.

The Argument Denying Congress' Power To Prohibit Interstate Commerce

The principal argument against the constitutionality of prohibitory
Congressional legislation pivoted on the dual conception of the Federal
System "The Federal Equilibrium". The Constitution, the argument ran,
clearly contemplates two spheres of governmental activity, that of the
States, that of the United States; and while the latter government is
generally supreme when the two collide with one another in the exercise
of their respective powers, yet collision is not contemplated as the
rule of life of the system, but the contrary. And since there are these
two spheres, the line to be drawn between them, in order to secure
harmony instead of collision, should recognize that the objects which
the National Government was established to promote are relatively few,
while those which the States were retained to advance comprise the
principal objectives of government, the protection of the public health,
safety, morals, and welfare. The power to promote these ends is, indeed,
the very definition of the police power of the States--that power for
which all other powers of the States exist. Seriously to impair the
police power of the