In 2004, Democrats won the working-class vote by 11 points; George W. Bush was reelected. In 2006, Democrats won the working-class vote by 22 points and took the House and Senate. In 2008, Democrats won by 22 points again, and President Obama was elected. In 2010, the margin narrowed to 11 points, and Republicans took the House back. In 2012, Obama was reelected—on the strength of another 22-point margin among voters making under $50,000.

“It doesn’t often get reported, but the key indicator that has been decisive for the last several elections is how people making below the median income vote,” Podhorzer said this week. Black or white, Asian or Hispanic, male or female, young or old, it’s that simple. To reach these voters, Podhorzer believes, candidates need to focus on the economic issues of the working class. “Economic populism decides who wins elections in America,” he said.

Now, as a union man, Podhorzer has an interest in encouraging politicians to cater to this demographic. But the data bears out his claim. In addition to working-class voters’ Democratic margin, their turnout rate is also an important variable. Though they make up half of all earners, they consistently comprise less than half of the electorate, because the richer people are, the more likely they are to vote.