President Donald Trump introduced his “discounted reciprocal tariffs” on over 200 countries on April 2. Most countries receive a base tariff rate of 10%, but for countries receiving more, the rates were calculated by halving a rate he displayed as “tariffs charged to the U.S.A. including currency manipulation and trade barriers.”

Ridiculed for imposing trade tariffs on frozen islands largely inhabited by penguins, Donald Trump's formula for calculating those levies has a serious side: it is also hitting some of the world's poorest nations hardest.