What’s behind the sudden outburst of populism in the Democratic Party?

Partly the weak economic recovery. Most economic indicators have turned positive — economic growth is up, unemployment down, the housing market is in recovery. But ordinary Americans are not feeling it. In last month’s CNN poll, two thirds of Americans said the nation’s economy was poor. More than half expect it to remain poor a year from now.

People at the top of the income ladder have been raking in the money while wage growth for working Americans has stagnated. That’s a recipe for a populist explosion.

Remember the “Occupy Wall Street” movement that started in 2011 and spread across the country? Most pundits don’t believe it had any impact, especially compared with the Tea Party. They’re wrong. In a stroke of marketing genius, the Occupy movement introduced the phrase “1 Percent” into the nation’s political vocabulary. That’s what defeated the Republican presidential nominee Mitt Romney in 2012. Romney was Mr. 1 Percent.

The Occupy movement won a big victory with the election of Bill de Blasio as mayor of New York in November. De Blasio’s issue was the growing economic inequality that’s painfully visible in New York City: gleaming new condominiums for the very rich alongside deep and increasing poverty.

“We are called,” De Blasio said in his inaugural address on Wednesday, “to put an end to economic and social inequalities that threaten to unravel the city we love.”