The extreme protective system which had been at the first a temporary expedient for aiding in the struggle for the Union, adopted hastily and without any thought of deliberation, gradually became accepted as a permanent institution. From this it was a short step, in order to explain and justify the existing state of things, to set up high protection as a theory and a dogma. The restraint of trade with foreign countries, by means of import duties of forty, fifty, sixty, even a hundred percent, came to be advocated as a good thing in itself by many who, under normal circumstances, would have thought such a policy preposterous. . . . The result was that the tariff gradually became exclusively and distinctly a protective measure; it included almost all the protective duties put on during the war, added many more to them, and no longer contained the purely revenue duties of the war.
— Frank W. Taussig, Tariff History of the United States  from Why Trade Retaliation Closes Markets and Impoverishes People by Jim Powell