The president’s plan for reciprocal tariffs sounds good in theory. But there was a reason the United States abandoned the approach a century ago. The gains would be few and the costs enormous.

President Donald Trump is likely to dust off a 1930 trade law largely forgotten for decades to back his new reciprocal U.S. tariffs that will match other countries' higher import taxes, trade and legal experts say.

Trump spoke to reporters from the Oval Office about his decision, saying it was an “amazing day.” When asked if prices would rise as a result of the tariffs, he said that they “could go up somewhat” at first, but then “prices will also go down.”