Historian Matthew Jacobson's work on the "alchemy of race" explains how the definition of "white" in America shifted in the 1920s to include previously excluded groups like Celts, Slavs, and Hebrews. This expansion was a strategic move to shore up a cultural majority against new immigrants and other racial groups. The hosts apply this historical context to modern figures like Barack Obama and Meghan Markle to illustrate how whiteness is a social construct tied to power and lineage.