How limiting is Walsh’s union cash?

Marty Walsh has received about $45,000 from firefighter unions.Pat Greenhouse/Globe Staff/file/Globe Staff

It was a top-tier tussle in the Boston mayor’s race, one marked by a bold gamble by one leading candidate, an encouraging emphasis on independence by a second — and a trust me stand that underscores the challenges facing the third.

The definitional drama started when Stand for Children, an educational advocacy group, endorsed John Connolly — and announced that it would spend as much as $500,000 promoting his candidacy. His rivals quickly demanded that Connolly disavow those outside dollars.

At a press conference on City Hall Plaza Wednesday, the city councilor did just that, asking both Stand and Democrats for Education Reform, another group that has endorsed him, to cease any expenditures on his behalf.

Good, but not good enough, declared Suffolk County District Attorney Dan Conley, who said Connolly should pledge to donate whatever amount any outside group spends boosting his prospects to the fund established to help victims of the Marathon bombing.

By day’s end, Connolly had done that, too. Asking Stand for Children to stand down was a smart move on his part. By doing so, he neutralized the issue — and demonstrated an admirable determination to win this race on his own.

Back to Conley, the DA. Noting that he himself had sought “very few” endorsements because of the premium he puts on political independence, Conley also turned up the heat on Marty Walsh, the other tenant of the race’s top tier.

“Just in the first two weeks in August, labor unions across the United States have poured money into his campaign,” Conley said. “So I call on Marty Walsh as well to do what John Connolly did today.”

That put the campaign spotlight squarely on Walsh. A state representative who also served as head of the Boston Building Trades Council, Walsh is the strong favorite of organized labor, which is making a huge push on his behalf. As the Globe’s Andrew Ryan has reported, by early August, unions had already given Walsh more than $170,000, mostly in big-dollar contributions. (Under state law, unions aren’t limited to $500, as individuals and PACs are). By month’s end, the campaign expects to have raised more than $1 million, of which 25 to 30 percent will be from unions.

In a Thursday sit-down, Walsh said he’ll neither reject (or offset) the big-dollar union contributions nor declare that he doesn’t want supportive groups like the firefighters to run independent-expenditure ads on his behalf.

Walsh stressed that he has more than 4,000 individual contributors. Still, his big haul of union money raises this question: What degree of independence would he bring to the mayor’s office? As we’ve seen before, powerful public-sector unions sometimes help create a dysfunctional political dynamic. Those unions help politicians get elected — and then push the politically beholden office-holder for wage-and-benefit packages (or other advantages) that aren’t affordable over the long term.

Further, it’s difficult to be both a union favorite and a determined reformer. To see why, consider the Boston Fire Department. It is, as Boston Municipal Research Bureau President Sam Tyler notes, “a department that clearly needs reform.” One reason it hasn’t been reformed is that Boston Firefighters Local 718 is a tough, aggressive, change-resistant union — one whose membership, incredibly, includes almost the entirety of the department’s command staff.

The Boston firefighters union has given Walsh $15,500; the state firefighters union (headed by a former Boston union president) has chipped in $15,000; add a similar contribution from the national union, and Walsh has received about $45,000 from firefighter unions alone.

I give Walsh credit for supporting lifting the cap on charter schools. But what assurance do average taxpayers have that, as mayor, he’d be tough enough to stand up to electoral allies like the firefighters? So far, little more than his declaration that he’s running to be mayor of all of Boston.

“I absolutely am going to be independent,” Walsh told me. “I am going to be a tough negotiator, but I’ll be a fair negotiator.”

Now, Walsh is a decent and likable guy — but also one who, as a state representative, has filed some reform-blunting union legislation.

In this race, it’s going to take more than vague talk to put worries about his independence to rest.