It was a Philadelphia underdog story: Irish American son of a firefighter from the old neighborhood, dismissed at first, captures Democratic nomination for mayor.

To some Democrats, former City Councilman Jim Kenney's landslide win also echoes nationally as the latest example of a progressive big-city tide - on the order of the 2013 victories of Bill de Blasio in New York and union laborer Marty Walsh in Boston.

These mayors and others were elected by broad, cross-racial coalitions, on promises to address the economic frustrations of workers and to end racial disparities in law enforcement.

"Putting people ahead of big corporate interests isn't just a winning formula for Philadelphia, it's what millions of voters across our country will be looking for in the months and years ahead," AFL-CIO president Richard Trumka said.

Kenney, for instance, vowed to raise the minimum wage, bolster public schools, and establish universal prekindergarten. He also highlighted his record of supporting LGBT rights and efforts to decriminalize marijuana possession, citing the disproportionate impact of drug laws on African Americans.

In New York, de Blasio highlighted his biracial family, promised to halt aggressive stop-and-frisk tactics in minority neighborhoods, and railed against the city's increasing unaffordability for all but the very rich.

"The economy has recovered in many ways, but a lot of people have been left behind, and that's more visible in cities," said Anna Greenberg, the pollster for both the Kenney and de Blasio campaigns, as well as Gov. Wolf last year.

"Populist, progressive mayors are leveraging city government, which has a direct impact on people's lives, to attack these problems," she said.

Issues of income and wealth inequality are also animating the discussion in the Democratic presidential race, pressuring front-runner Hillary Rodham Clinton to move leftward on economic issues. The party's congressional wing is resisting President Obama's push for a free-trade agreement with Pacific Rim nations.

Kenney faces Republican Melissa Murray Bailey and a possible independent challenge from Bill Green, a former city councilman and member of the School Reform Commission. But Kenney is considered the prohibitive favorite in the overwhelmingly Democratic city.

Most striking in his victory was the cross-racial appeal.

It appeared that Kenney won a plurality of the votes in the 30 predominantly black wards in the city, according to an Inquirer analysis of the vote. He is white; State Sen. Anthony Hardy Williams is black, and seemed to count on traditional racial voting patterns.

Greenberg said her polling showed that marijuana decriminalization was a breakthrough issue for Kenney, communicating to black voters that he understood the impact of harsh drug laws and unequal enforcement in minority communities.

In addition to his policy positions, Greenberg said, Kenney peeled off the endorsements of prominent African American political leaders in Northwest Philadelphia, City Councilwoman Marian B. Tasco and State Rep. Dwight Evans.

"Williams' message at the end seemed to be 'I'm African American,' " said Bill Hyers, the strategist who advised Philadelphia Forward, one of the independent-expenditure groups that backed Kenney.

"Voters don't vote on the basis of race as much as they did back in the day," Hyers said. "The guy with the best message is going to get votes from everywhere. He may not win a group, but he'll get his share and build a coalition. You've got to talk about your vision going forward."

Hyers was de Blasio's campaign manager and ran Mayor Nutter's successful come-from-behind campaign in 2007, when he captured a large share of white voters.

After November, Philadelphia will be the latest large majority-minority city to be led by a white mayor, joining New York, Los Angeles, and Chicago, where Rahm Emanuel was just reelected. (Boston is majority white, as is its mayor, Walsh).

A poll conducted for The Inquirer just before the primary found that 43 percent of those who were planning to vote identified themselves as liberals. Among that group, Kenney was viewed favorably by 70 percent, unfavorably by 25 percent.

The survey accurately forecast a blowout for Kenney.

Still, pollster Adam Geller, of National Research Inc., said he was not prepared to conclude that Kenney is part of a left-leaning trend.

"A lot of forces coalesced in his favor," said Geller, a Republican. He noted that Williams and Lynne M. Abraham ran weak campaigns. "Kenney ran a good, smart political campaign for a Democratic primary - they knew who they wanted to target and how."

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@tomfitzgerald