Donald Trump has flip-flopped on many issues: Today, he says he’s pro-life; in 1999, he said, “I’m very pro-choice.” Last year, he said Republicans should “never give up!” on trying to repeal Obamacare; during September’s presidential debate, he said, “I saved it.” Three years ago, he said Bitcoin “seems like a scam”; now he wants to make America the “crypto capital of the planet.”

But Trump’s desire for high tariffs has been consistent. In an interview on Tuesday at the Economic Club of Chicago, he said, “To me, the most beautiful word in the dictionary is ‘tariff.’” As president, he called himself “a Tariff Man.” In fact, he imposed substantial tariffs when in office. Those actions were, however, mild compared with the tariffs he is proposing now. He initially suggested a 10 percent tariff on all imports, but now he talks about tariffs as high as 20 percent. (In Chicago, he even mused about 50 percent.) He wants a 60 percent tariff on imports from China.

Most economists believe that this would be a terrible idea, and I share that view. I’m not a free-trade purist; I opposed the Obama administration’s proposed Trans-Pacific Partnership and have been generally supportive of the much tougher line the Biden-Harris administration has taken on trade.

But there’s a big difference between sophisticated, limited deviations from free trade and Trump’s desire to put what he called a “ring around the collar” of our economy.

It has never been entirely clear why Trump has a thing for tariffs. My guess is that he sees everything in terms of winners, losers and punishment: If we buy more from foreigners than they buy from us, that in his mind makes America a loser, and he wants to punish foreigners by making them pay for access to the U.S. market. Whatever he’s thinking, restoring the good old days of high tariffs is one of Trump’s key policy obsessions, and high tariffs are very likely to become a reality if he wins the election.

And when I say the good old days, I mean old. High tariffs were a consistent feature of American policy from the Civil War through 1933, but in 1934 we turned to a policy of reducing tariffs on other countries’ exports in return for lower tariffs on our exports.