The Trump administration argues that it can set tariffs however it likes by relying on a maximalist reading of the International Emergency Economic Powers Act, or IEEPA. That 1977 law, allowing the president to regulate international commerce after declaring a national emergency, has been the underlying justification for many American sanctions—including those Ronald Reagan imposed on apartheid South Africa in 1985 and those Joe Biden placed on Russia after it invaded Ukraine in 2022. Although the law is supposed to be invoked only in cases of “unusual and extraordinary” threats, presidents have regularly relied on IEEPA for extended durations because of the broad authorities that it grants them. The state of emergency originally declared by Jimmy Carter during the Iran hostage crisis of 1979 has been annually renewed up to the present day.