For the most part, Americans outside of New York have heard only one story about New York City’s mayoral race — the bizarre public self- immolation of former representative Anthony Weiner. But obscured beneath the flood lights of the Weiner farce is a populist insurgency that exemplifies the coming struggle to define the Democratic Party in the wake of President Obama.

The progressive champion in the race, New York Public Advocate Bill de Blasio, is challenging the odds-on favorite, City Council Speaker Christine Quinn, to succeed retiring Mayor Michael Bloomberg. Under pressure from de Blasio and progressives, she has begun recently to assert some independence from Bloomberg’s trickle-down technocratic politics and shown a willingness to challenge the administration on certain issues, such as the city’s harmful homelessness policies. But Quinn has too often used her influence as speaker to protect corporate and developers’ interests.

De Blasio has pitched his campaign with the most populist and ambitious agenda in memory. He does so in a city that is one of the most unequal in the country, with an extreme gulf in income and wealth. Visitors gape at Manhattan’s skyscrapers, but almost half the population lives at or near the poverty level. In any one year, 1.5 million suffer hunger or food insecurity. Accelerating gentrification has made affordable housing scarce. Public schools are in crisis. Bloomberg has vetoed efforts to pass a living wage, and he is so anti-labor that all of the 152 public unions in the city now are without a contract.

De Blasio argues that New York is a “tale of two cities,” and that the central issue of this and future campaigns is “economic fairness.” “Without a dramatic change of direction,” he said in a May 30 address, “an economic policy that combats inequality and rebuilds our middle class, generations to come will see New York as little more than a playground for the rich.”

De Blasio preaches that this isn’t necessary and it isn’t right, suggesting that New York City should be a “laboratory for progressive government.” He champions passage of a living wage and paid sick days. He seeks a mandate for a city tax on incomes of more than $500,000 to fund universal preschool for New York children as well as after-school academic and athletic programs for middle schoolers. He calls for imposing affordable housing requirements on luxury developers, promising to save or build 200,000 affordable housing units over the next decade.

Married to Chirlane McCray, an African American with two children in public schools, de Blasio argues that his “tale of two cities” is most stark in racial profiling. A white teenager can walk down the street without being hassled. Concerned African American and Latino parents warn their children to expect to be stopped and possibly frisked for no reason. De Blasio has demanded an end to racial profiling, promoting a law that would transform the training and practices of the New York City police, and promises to replace police commissioner Ray Kelly, who tenaciously defends the stop-and-frisk policy.

De Blasio sees his campaign as part of the effort to reclaim the progressive tradition. As he put it in an interview with Joan Walsh, “From FDR through Johnson, including Eisenhower . . . government was going to play an active role. We were going to spur on the economy. We were going to make sure there’s some fairness in distribution. And there was a lot of smart growth that came out of that.”

As the Nation magazine, where I serve as editor, wrote in its endorsement, de Blasio’s commitment to “reimagining the city in boldly progressive, egalitarian terms” offers voters a “once-in-a generation opportunity to rewrite the narrative of their city.”

Nine candidates now vie to replace Bloomberg. While Tuesday’s Quinnipiac University poll shows de Blasio running ahead of Quinn, most polls show him in a virtual tie for second with former city comptroller Bill Thompson, a moderate African American who challenged Bloomberg in 2009. Quinn has the name recognition, much establishment backing and would be the first woman elected to lead the city. But she’s running far below the 40 percent of the vote need to avoid a run-off. If de Blasio can make the run-off, he would finally have the opportunity to put his case to voters.

In the post-collapse, post-Occupy, post-Obama world, Democrats are headed into a fierce battle over the direction of the party. Obama forged his new majority largely on anti-war, socially liberal causes — aided by Republican reaction in contrast. But the Democratic Party’s consensus around social issues and diversity has masked a growing divide on economic issues between the Wall Street wing of the party and a populist wing that is beginning to stir. The mayor’s race in New York City is an early entry in this debate about the future of the party and the country. May it not be obscured by Weiner’s spectacular flameout.

Read more from Katrina vanden Heuvel’s archive or follow her on Twitter.