A labor arbitrator defined Boston’s mayoral race before either candidate hoping to succeed Tom Menino had a chance to do so. The 25-percent raise for the police patrolmen’s union, now awaiting approval at the City Council, has knocked Rep. Marty Walsh back on his heels, and exacerbated tensions around Walsh’s ties to organized labor. Tuesday’s mayoral debate saw Walsh continuing to fight off attacks by his opponent, John Connolly, on issues connected to the contract award. But the debate also showed that, even if the arbitration award hadn’t dropped into the race, Walsh would likely still be experiencing tough sledding.

The Dorchester legislator is trying to sell a campaign narrative that’s grounded in his work on Beacon Hill – a place that operates by keeping lawmakers focused on small-bore issues, and stifles any sort of debate or big thinking.

CommonWealth’s Spring 2012 issue detailed the sclerosis that’s taken hold of the Legislature over the past two decades. Lawmakers in both houses are spending far less time meeting, and debating, than they did 20 years ago. They’re taking far fewer votes. And the votes they do take often arrive with outcomes predetermined by a small group of legislative leaders. Legislative leadership has consolidated political power and policy decisions, at the expense of committee chairs and rank-and-file lawmakers. Legislators have been forced to distinguish themselves through constituent services and small-bore matters, because that’s all the State House’s culture permits.

Tuesday’s mayoral debate showed the difficulties in using the modern Legislature as a launching pad for higher office.

Walsh was at his best when speaking as an empathetic everyman. For instance, Connolly answered a question about foreclosures by talking about a city-run program, while Walsh lamented the plight of the scores of city residents “living week to week, paycheck to paycheck. You miss a paycheck, you miss a month’s worth of pay – that’s a lot of money to a lot of folks – you’re going to fall behind and never catch up.” These moments came too infrequently. Walsh often appeared to be trying to out-debate Connolly at every turn, instead of focusing on sending targeted messages to women, progressives, and communities of color.

The longer the debate dwelled on policy minutiae, the more Walsh got the worst of the exchanges. He cited votes funding biotech and enabling turnaround schools, but voting for a finished bill isn’t the same as leading a policy charge – especially on Beacon Hill, where the real debate happens behind closed doors, among a small group of politicians. Walsh sounded out of his depth when trying to go toe-to-toe with Connolly on education legislation, and that’s because Beacon Hill’s power structure purposefully placed education policy outside Walsh’s wheelhouse.

The exchanges on transportation finance were especially telling. The Legislature recently passed a transportation finance package that plugs immediate operating shortfalls, but leaves many key capital projects unfunded. It did this because suburban lawmakers worried about plowing money into the MBTA, and because House Speaker Robert DeLeo decided that Massachusetts couldn’t afford the full cost of maintaining its transportation systems. That assertion was based more on gut feeling than actual data, but it ruled the day, even among urban lawmakers like Walsh.

Beacon Hill’s unwritten rules demanded that lawmakers like Walsh not buck DeLeo on transportation finance. But playing by Beacon Hill’s rules left Walsh open to attack on Tuesday, and Connolly took full advantage.

“The folks on Beacon Hill let us down a lot,” Connolly complained.

“The Legislature passed legislation that allowed the system to be upgraded,” Walsh replied. “There was no ball-dropping by the Legislature.”

This came minutes after he’d complained that a key bus route only passed through Codman Square once an hour. Connolly shot back that the transportation bill Walsh voted for “didn’t do enough,” and that lawmakers had been neglecting Boston’s transportation needs for “a whole bunch of years.” Money was so tight that the city was now depending on corporations like New Balance to pay to expand the transit system. Walsh’s rebuttal – that he’d successfully lobbied for the renovation of four Red Line stations and the expansion of a rail line in his district – didn’t alter the math the men were arguing about. But it’s all he could offer.

Paul McMorrow comes to CommonWealth from Banker & Tradesman, where he covered commercial real estate and development. He previously worked as a contributing editor to Boston magazine, where he covered...