Last week Mayors Against Illegal Guns kicked off a 100-day, 25-state bus tour meant to both acknowledge lawmakers who voted for reform and ratchet up the pressure on those who did not.
On a conference call with reporters last Wednesday, John Feinblatt, a chief policy adviser to Bloomberg, said attempts to turn the attacks back on the mayor would prove ineffective.
"When senators want to make this about Mayor Bloomberg, what they're really trying to do is change the subject," he said. "This isn't about Mayor Bloomberg."
But that's exactly what both Democrats and Republicans who have found themselves on the receiving end of the Bloomberg-backed ads are trying to do. In recent weeks, Pryor released a television commercial in Arkansas lambasting the mayor, himself.
"No one from New York or Washington tells me what to do," the vulnerable Democratic senator says in the spot. "I listen to Arkansas."
Ayotte, who has been a frequent target of Bloomberg's group, now regularly features the New York mayor in her fundraising appeals.
"Bloomberg and his radical allies are going to great lengths to try to discredit me, and it's appalling," Ayotte wrote in an e-mail message to supporters last week. "They think that I'm an easy political target, but they're messing with the wrong senator."
Outside groups have joined the fight too. Last week, pro-Ayotte forces attempted to turn the tables on Mayors Against Illegal Guns, by casting Bloomberg in the role of bogeyman.
An ad released by the conservative American Future Fund focused almost entirely on tarnishing the mayor's image.
"Michael Bloomberg is New York's ultra-liberal mayor. He's worth $27 billion. His company is embroiled in scandal," the ad's narrator says. "Bloomberg tells New Yorkers how much they can drink and now spends millions telling New Hampshire what to think."
The American Future Fund is attempting to tap into the same independent-mindedness of voters in the "live free or die" state that led the New Hampshire Union Leader to take a swipe at Bloomberg in a recent editorial.
"Our advice to Mayor Mike: take a big gulp and go away," it read. "Neither Kelly Ayotte nor Granite Staters will be intimidated by the likes of you."
But at least one Democrat pointed out that a public battle with Bloomberg might actually not be all that bad.
"In Alaska, having a New York mayor tell us what to do? The guy who wants to ban Big Gulps?" Alaska's Sen. Begich said in an interview with The New York Times last week. "If anything, it might help me." ABC's Jeff Zeleny and Joan Greve contributed reporting.