With less than a month in office, the president has pursued trade actions that could shatter the global trading system and dwarf the trade measures he took over his entire first term.

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.

US President Donald Trump has ordered advisers to develop a new tariff system that reflects foreign countries’ trade barriers, taxes, and subsidies. The plan, expected by April 2, aims to counter what Trump calls unfair trade practices and push companies to manufacture in the US.