The winning path in Boston’s 12-way scramble for mayor travels first through a candidate’s core base of supporters, but has to branch out from there to less familiar terrain. Which is why Marty Walsh found himself standing on Monday night in a sweltering Jamaica Plain meeting room accented with a rainbow mural, large puppets perched in the corners, and a “Save the Rainforest” poster on the wall.

It was a long way from the Laborers Union hall in Dorchester, where Walsh cut his teeth in politics. But the affable Dorchester state rep is determined to show that the gulf isn’t quite as large as it might seem between his strain of union-driven populism and the left-leaning preferences of Jamaica Plain’s politically-charged denizens. So his campaign brought this week’s installment of a series of town meetings dubbed “Mondays with Marty” to Spontaneous Celebrations, a community arts center whose course listings include “toddler drumming” and other offerings that telegraph why this is Boston’s most Cambridge-like neighborhood.

It wasn’t entirely smooth sailing with the crowd of about 50 residents, a group eager to pin candidates down on their stands – and not generously inclined toward those that tilt against liberal orthodoxy.

Walsh talked about education in his opening comments, but seemed to carefully elide the issue of charter schools in a room not likely to be friendly to them. As if on cue, the first question from the issue-attuned audience: What about charter schools? Walsh explained that he supports lifting the cap on charters, saying they have been a much-sought alternative to district public schools, and touted his role as a founding board member at the Neighborhood House Charter School in Dorchester.

When a middle-aged black woman, one of only a couple of minorities in the overwhelmingly white crowd, asked how he would address racism in Boston, Walsh seemed flummoxed, saying it was the first time that question had come up during three-and-half months of campaigning. Walsh went on to say racism would have no place in his administration, and boasted of representing one of the most diverse districts in the state. But convening citywide race dialogues just isn’t in the makeup of the 46-year-old son of Irish immigrants, whose everyman persona may make him the most Menino-like candidate in the mayoral field.

State Rep. Liz Malia, left, chats with mayoral candidate Marty Walsh following Monday’s forum.

Like the man he’s looking to succeed, Walsh is more a man of deeds than quick-on-his-feet words. And so it was his right-hand campaign alter ego, Joyce Linehan, who jumped up and cut the thickening air with a suggestion that Walsh talk about his work leading a program that brings minorities and women into the union building trades.

He did, and it was music to the crowd’s ears.

“A lot of people in JP will be very pleased with that. I know I was,” said Rosemary Jones, of Walsh’s talk about helping women and minorities enter the building trades. Standing outside the hall after the forum, the 40-year neighborhood resident pointed to something else that is likely to make a positive impression on people in JP: the support Walsh has from the neighborhood’s local state rep, Liz Malia.

His endorsement by Malia, an openly gay liberal lawmaker, is a huge coup for Walsh. Malia, a very visible presence at Monday’s event, says Walsh has been a stalwart ally on many issues, but singles out two in particular. His work on behalf of substance abuse issues resonates strongly with Malia, who co-chairs the Legislature’s Mental Health and Substance Abuse Committee — and shares with Walsh a personal background as someone in recovery. But it is his support a decade ago for marriage equality, something Walsh cites as his proudest moment in office, that Malia says shows a side to her House colleague that may surprise those who pigeonhole him as an old-school labor leader.

“He stood up and took a lot of arrows from his constituents,” Malia said following the forum. The gay marriage forces had a lot of lawmakers from districts like hers, she said. “What we needed was someone who could build bridges to reps in other communities. He was a real leader.”

Trying to attach labels to candidates in the race is tricky business. When a Boston Herald/Suffolk University poll earlier this week pegged John Connolly, Walsh, Dan Conley, and Rob Consalvo as the early leaders in the mayoral race, the paper remarked that no minority or “so-called ‘progressive’ candidate” cracked this top group.

But one of the biggest changes in the city’s political dynamic is the degree to which the center of gravity has shifted to the left. WGBH’s Adam Reilly wondered yesterday whether the poll frontrunners would agree with the Herald characterization, and found that they all rejected it and readily embraced the progressive banner.

“People tend to have a bias or prejudge me,” Walsh said after Monday’s JP forum. “I’m as, if not more, progressive than anyone in this race.”