Hillary Clinton and Bernie Sanders are promising all types of programs to make America a more equal country. That’s no surprise. But when you look at performance and not rhetoric, the administrations of political progressives have made the distribution of income more unequal than their adversaries, who supposedly favor the wealthy.

The Census Bureau releases annual updates on income distribution in the U.S., publishing three technical statistical measures—the Gini index, the mean logarithmic deviation of income (mean log deviation...