Do Americans have too many jobs? Democratic Socialist congressional candidate Alexandria Ocasio-Cortez said last week that “unemployment is low because everyone has two jobs” and “people are working 60, 70, 80 hours a week and can barely feed their family.” Sen. Elizabeth Warren said people are “working minimum wage jobs that won’t support them or they’re working two, three or four jobs.”

But Bureau of Labor Statistics data show only a small minority of Americans work multiple jobs. That percentage has been around 5% of working...