Historian Jim Powell explains, in FDR’s Folly: How Roosevelt and His New Deal Prolonged the Great Depression:

Considering how passionately New Dealers condemned monop­olies, it’s curious that FDR didn’t mount a major assault against the Smoot-Hawley tariff that Hoover had signed into law back in June 1930. … Tariffs were long viewed as “the mother of trusts” because they limited choices for consumers and enabled domestic companies to charge prices above world market levels.

Ironically, the Sherman Antitrust Act (1890), the New Dealers’ favorite remedy for fighting monopoly, was originally enacted to provide political cover for the McKinley tariff (1890), which raised tariffs to higher levels. New York attorney Franklin Pierce explained the game in his 1913 book The Tariff and the Trusts: “We legalize conditions [high tariffs] out of which an evil arises and then attempt to suppress the evil by penal statutes. We provide for high duties upon foreign imports for the protection of home industries, and when a monopoly controlling the home market results therefrom, then pass penal laws punishing the monopoly. In this way our politi­cians prove to the great combinations who furnish campaign disbursements for political parties their fidelity to monopolistic interests, while, by the penal statute, they assure the people that they are against trusts.”

Read more of Pierce’s 1913 book here.