The US already has tariffs on a few sectors. It hasn't gone that great

Since the 1960s, the U.S. has charged a 25% tariff on imported pickup trucks. The extra protection from foreign competition encouraged U.S. automakers to concentrate on pickup trucks while largely ceding the market for cheaper, smaller vehicles. (Jeff Kowalsky/AFP)

For decades, the United States has generally kept tariffs low and promoted free trade, but a few domestic industries have long been protected by import taxes and other trade barriers.

Now, as President Trump prepares to announce another big round of tariffs, these sheltered American industries offer clues about how those import taxes could work out for the rest of the country.

Trade barriers can prop up domestic industries. But they also raise prices, distort markets and leave the U.S. vulnerable when home-grown supplies run short. Here are three examples of how protectionist policies can lead to unintended consequences.
The not so sweet tax on sugar