President Donald Trump on Thursday imposed once unthinkably high U.S. taxes on imports from dozens of countries, part of his campaign to turn one of the world's most open economies into a fortress bristling with barriers to trade.

The U.S. has concluded trade frameworks with top trading partners including the European Union, Japan and South Korea. But deals with others remain works in progress, and Trump is also targeting specific industries like semiconductors that are used by millions of Americans across a wide range of products.