"First. It is unnecessary to repeat what has frequently been said by this court with respect to the complete and paramount character of the power confided to Congress to regulate commerce among the several states. It is of the essence of this power that, where it exists, it dominates.
Interstate trade was not left to be destroyed or impeded by the rivalries of local government. The purpose was to make impossible the recurrence of the evils which had overwhelmed the Confederation, and to provide the necessary basis of national unity by insuring 'uniformity of regulation against conflicting and discriminating state legislation.'
"It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely, by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce."
-- Mr. Justice Hughes, the Shreveport Rate Case, 20 years before FDR's "New Deal Commerce Clause".
This is a case dealing with actual commerce and regulation of rail rates. This is entirely consistent with the original intent of the Commerce Clause, in that it deals with regulation required to establish an efficient infrastructure necessary for the process of commerce to take place. Find a case where Congress seeks to regulate something that is neither being bought or sold, on the grounds that it is "potentially interstate commerce" prior to the New Deal, and you'll have a case.