“It’s the economy, stupid.” The words date from Bill Clinton’s 1992 presidential campaign, but the basic idea that political shifts are the visible manifestations of hidden economic developments was first articulated by Karl Marx, who wrote before the word “economy” had its current meaning. When he declared, in 1848, that “The history of all hitherto existing society is the history of class struggles,” the notion was truly revolutionary. It has become a commonplace. Pundits ferret out economic causes for everything, politicians strive to present voters with economic good news, and careful studies show that economic trends influence elections.