For decades, William Darity Jr. and Darrick Hamilton toiled in obscurity. They criticized mainstream economists and politicians for failing to address racial inequality, and touted more radical remedies of their own.

Now, with the 2020 presidential campaign under way and liberal Democrats ascendant, the two economists are in the spotlight, thrust into the middle of an intraparty debate over how much to embrace big government and a race-oriented message.

Their...