Marty Walsh’s union background is his great curse and his blessing. It helped him assemble an army of campaign volunteers who helped propel him to a first-place finish in last month’s 12-way preliminary, and it’s what gives him the liberal cred that has some left-leaning types lining up behind him over rival John Connolly in the final election match-up. But it’s also the connection that poses the biggest threat to his man-of-the-people candidacy, a campaign banking more on his affable down-to-earth persona than policy particulars.

That tension provided the only real moments of drama in yesterday’s first of three televised showdowns between Connolly and Walsh. They have staked out similar positions on many issues facing the city, with the two campaigns sometimes devolving into a comical soup of political correctness, an ironic backdrop after all the handwringing about two white guys emerging as the mayoral finalists.

But when moderator Jon Keller posed a question about looming pension liabilities, it didn’t take long for Connolly to migrate the discussion to Walsh’s sponsorship of legislation on Beacon Hill that would eliminate any power of communities to reject a binding arbitration award for police or firefighters that local leaders deem excessive or unaffordable. Walsh’s bill would strip away the City Council’s ability to reject the $80 million arbitration award recently granted to Boston patrol officers, a decision that both candidates say asks too much of city taxpayers.

Connolly said Walsh’s bill would cut into the city’s ability to fund pre-kindergarten, longer school days, or park renovations. Walsh gamely argued that, with his good relations with unions, negotiations would never get to binding arbitration under his administration. At one point, he tried to shift the conversation to the federal government shutdown crisis in Washington, and he eventually made it clear that he’d like to move on and talk about almost anything else.

Walsh has been labor’s go-to guy in the Legislature. His personal tales of overcoming adversity and his union background help the Dorchester state rep come off as a scrappy fighter for the underdog. Some public-sector union battles, however, look more like a special-interest grab at limited public dollars than a social justice cause that liberal voters will rally around. Which of these competing views colors his candidacy more will make a big difference.