Sitting in a 12th floor office building overlooking City Hall, two of Nelson Diaz's staffers prepared him on how to pitch a room full of Millennials that evening.

"We want you to get across that you were progressive before it was cool, outside of public office, without supportive legislators," said campaign manager Ian Rivera. "You did it when it was difficult and when you took heat for it."

Rivera and communications director Barry Caro, both in their late 20s, told Diaz, 68, to focus on his commitment to fixing Philadelphia schools, his rise from Harlem tenement to Temple Law School, and his record of civil rights activism - much of which occurred long before the voters he'd be addressing were born.

Diaz, a former Common Pleas Court judge, whose resumé includes posts at the Department of Housing and Urban Development and the White House, is aiming to position himself as the original progressive candidate.

In interviews, he hearkens back to the 1970s, when he led a group of black and Latino students picketing against the Temple University administration. He went on to cofound the school's first black and Hispanic student association, and became the first Puerto Rican to pass the Pennsylvania bar exam in 1973, he said. In 1978 he marched in support of the Equal Rights Amendment and a few years later, sat on the first-ever Pew research council studying AIDS.

With fourteen weeks until the May 19 primary, Diaz says he's miffed at his early characterization as a longshot candidate. He was in the middle of the fund-raising pack - but well behind the highest - in campaign contributions for 2014. He has no major endorsements, but boasts a career of public and private executive experience arguably unmatched in the field.

"When I look at each one of [the challengers], I don't see anyone who has run anything - they are lobbyists, legislators, spokespersons, activists, a prosecutor," he said. "I don't see anyone that has that leadership experience, I think that's really important."

Diaz worked as an aide to Vice President Walter F. Mondale and served as general counsel to HUD, where he oversaw more than 500 attorneys. In Philadelphia, Diaz was administrative judge of Common Pleas Court and is partly credited for decreasing case backlog and reforming the system. His last government post was as city solicitor, from 2001 to 2004 under Mayor John F. Street.

Since then, Diaz has worked as a partner at the Dilworth Paxson law firm and as a member of the board of directors at Exelon, which gave his campaign $10,000 in 2014.

"I think being away from and not part of the elected political framework of the city is good," said former at-large City Councilman Angel Ortiz, who pushed Diaz to run. "It means he's outside of the game, but it also means he hasn't dealt with ward leaders and that sort of thing for like 25 years, so it's a brand new world to get back into."

With freezing temperatures throughout much of February, there has been minimal door knocking for Diaz, a Chestnut Hill resident. A plan to greet commuters at the Temple Regional Rail station was canceled due to the frigid cold, and public campaign events numbered only one last week, with mornings and afternoons booked up with union endorsement meetings and fund-raising call time.

As the first Puerto Rican to run for mayor, Diaz said, he has the Latino base on lock. He thinks he can get votes from progressives and a portion of the African American community, particularly traditional public school advocates who may be against state Sen. Anthony Hardy Williams' stand in favor of school vouchers.

Diaz said he supports "charters that work," and sits on the board of one in Camden, but wants a moratorium on new charters until Philadelphia's school district can climb out of its financial crisis. He also is calling for an end to the School Reform Commission, though he's unclear on whether a mayor could dismantle the state-constructed entity.

Diaz credits education with his success in life. A community baseball league and a good school raised his grade point average from a D to an A when he was 15 and local gangs were grasping for him. His 89-year-old mother still has the report cards to prove it, he said.

"There's a feeling among the general popular-opinion-setters in this city that coming from the Puerto Rican community makes him not a viable candidate because Puerto Ricans and Latinos don't vote," Ortiz said, noting that the Latino turnout rate is similar to those of other ethnicities. "It's as if Nelson were only trying to attract that block or something. He's going after everyone."

At the Millennial event last Tuesday night, Diaz walked into an overheated room of young adults sipping cocktails. He wiped his brow with a napkin and launched into some of his promises for the city: safer streets, better jobs, a school system worth sticking around for.

He recounted marches from decades past and offered a campaign pledge that elicited cheers from the crowd:

"We're going to keep the city open 24/7 so Millennials can party whenever they want to. You study all night, work all day, you want to get out there. . . . You want to dance some salsa?" he asked. "I'll be happy as the mayor, with my wife, to teach you how to do some salsa."