The New Deal's "substantial effects" interpretation of the Commerce Clause is basically an open-ended assumption of authority by the federal government.
"The question comes to this, whether a power, exclusively for the regulation of commerce, is a power for the regulation of manufactures? The statement of such a question would seem to involve its own answer. Can a power, granted for one purpose, be transferred to another? If it can, where is the limitation in the constitution? Are not commerce and manufactures as distinct, as commerce and agriculture? If they are, how can a power to regulate one arise from a power to regulate the other? It is true, that commerce and manufactures are, or may be, intimately connected with each other. A regulation of one may injuriously or beneficially affect the other. But that is not the point in controversy. It is, whether congress has a right to regulate that, which is not committed to it, under a power, which is committed to it, simply because there is, or may be an intimate connexion between the powers. If this were admitted, the enumeration of the powers of congress would be wholly unnecessary and nugatory. Agriculture, colonies, capital, machinery, the wages of labour, the profits of stock, the rents of land, the punctual performance of contracts, and the diffusion of knowledge would all be within the scope of the power; for all of them bear an intimate relation to commerce. The result would be, that the powers of congress would embrace the widest extent of legislative functions, to the utter demolition of all constitutional boundaries between the state and national governments. "
Joseph Story
Commentaries on the Constitution
A thinker of his time, that Story guy. I wonder if he ever thought Congress would manage to make his nightmare come true, without a Constitutional amendment? He certainly would have known they would try, but probably expected the people sheep to rise up and swat them if they did.