Why the populist wave is setting the tone for Democratic candidates

Some moderate candidates have held back from populism, others have stretched the definition, but many are adopting the redefined populist rhetoric

When the Massachusetts senator Elizabeth Warren spoke in a New Hampshire town hall last month, she promised to break up Silicon Valley monopolies and levy a wealth tax on “the Rembrandts and the diamonds” of the super-rich, before quipping: “I’m sick of freeloading billionaires.”

Days earlier, the Vermont senator Bernie Sanders had addressed a rally in Concord, 45 miles west. He said his was a campaign that “tells the...