For American companies making such products, it came as a relief.

Southwire, a company in Carrollton, Ga., that makes power cable, and one of the largest manufacturers calling for the new tariffs, said the measures were necessary to ensure fair competition in the market for aluminum wire.

“We continue to believe that when there is a level playing field, the strength of our manufacturing comes forth,” said Burt Fealing, Southwire’s general counsel.

For economists and trade experts, however, the development was an “I told you so” moment.

Economists have long argued that by raising the price of steel and aluminum, Mr. Trump’s tariffs would make it more expensive to produce things like nails or cars in the United States — and would encourage companies to import more of those items, rather than making them in the United States.

Chad Bown, a senior fellow at the Peterson Institute for International Economics, called this an example of “cascading protectionism” that he said was “entirely predictable.”

“Trump’s steel and aluminum tariffs have raised the cost of key inputs, making American companies that rely on those metals less competitive worldwide,” Mr. Bown said. “Now Trump is expanding his tariffs to shield their products from competition as well. Where will it end?”