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.

Trump has argued that tariffs are an effective tool to incentivize manufacturing goods in the U.S. as well as protecting jobs and encouraging consumers to purchase domestic-made products. He’s also leveraged tariff increases to address the flow of illicit drugs and illegal immigrants across U.S. borders.