Last week the Obama campaign began airing its first ad targeting Mitt Romney's time as governor of Massachusetts, charging that he had "one of the worst economic records in the country."

Chicago released its second Massachusetts-themed ad today, repeating that charge from its first commercial but this time opening with a slam on Romney's fiscal record.

“When Mitt Romney was governor, Massachusetts was number one – number one in state debt,” the narrator says. “At the same time, Massachusetts fell to 47th in job creation, one the worst economic records in the country.”

Romney's campaign has pushed back on that characterization of his governorship. But this isn't just about driving home Romney's liabilities on key issues — it's also about muddying the water on some of the Republican's standard attack lines. Obama will probably never have the advantage on spending and size-of-government issues, so the next-best thing would be convincing voters that Romney doesn't have much high ground to claim there.