Medicare for All Is Defining the 2020 Democratic Race

A decade ago, Democrats in Congress were deep into the process of designing and debating the health care law that would become Obamacare. Tea Party protests were about to spring up around the country in opposition to the law. And President Barack Obama was on the verge of delivering a major address defending the law from its critics, and hoping to rally support from his own party.

In that speech, Obama positioned his approach as a middle ground between two extremes. "There are those on the left," he said,...