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.

Since the 1960s, tariffs — or import taxes — have emerged from negotiations between dozens of countries. Trump wants to seize the process. “Obviously, it disrupts the way that things have been done for a very long time,