Ever since the failed Senate vote on a background check compromise two months ago, Michael Bloomberg's anti-gun violence group has spent millions eviscerating Republican senators including Kelly Ayotte of New Hampshire and Jeff Flake of Arizona for voting against it.
But in recent weeks, the wealthy New York mayor has signaled a greater willingness to expand the attacks across the aisle by taking on the Senate Democrats who also rejected the bi-partisan deal. Although his tactics are increasingly drawing criticism from senior Democrats, Bloomberg has shown no signs of backing down.
In May, Bloomberg's group, Mayors Against Illegal Guns, unveiled a television ad campaign against one of those senators, Mark Pryor, D-Ark., and last week Bloomberg told hundreds of big-money Democratic donors not to open their wallets for Pryor or for the three other Democrats (Montana's Max Baucus, Alaska's Mark Begich and North Dakota's Heidi Heitkamp) who voted against the background check compromise.
On Capitol Hill last week, several key senators -- including Majority Leader Harry Reid -- expressed their displeasure with Bloomberg's aggressive approach.
"I spoke to the mayor this week -- he and I have been friends for some time -- to remind him just as I've reminded everyone here that to have Republicans in control of the Senate is a sure sign we will never ever get anything done," Reid said.
In an interview with Time Magazine, Sen. Chuck Schumer, D-N.Y., also sounded the alarm.
"Frankly, I don't think Bloomberg's ads are effective," Schumer said. "The mayor of New York City putting ads against people in red states is not going to be effective."
Even Sen. Joe Manchin, D-W.Va., one of the architects of the failed background check bill, was critical.
"There's going to be an election in 2014. That's the time, when we've exhausted every other avenue of getting the message out. Then do what you've got to do," Manchin told reporters on Capitol Hill last week, suggesting that Mayors Against Illegal Guns would be better off running ads debunking gun lobby talking points about his legislation. "We just need a little bit of help."
But Bloomberg's tactics should not have come as a surprise to Democrats. In March his gun control group unleashed a $12 million advertising campaign aimed at persuading 15 senators to vote to tighten U.S. gun laws. The targets included Pryor and Heitkamp as well as Indiana's Joe Donnelly, Louisiana's Mary Landrieu, and North Carolina's Kay Hagan -- all Democrats. (Ten of the targets were Republicans).
Bloomberg has dismissed the outcry from angry Democrats.
"I think at the moment we are running more ads against Republicans than Democrats but let me just point out this is not a partisan issue," Bloomberg said last week, according to the Washington Post. "If you vote to continue the carnage on our streets I don't care what party you're in. To bring in partisanship when you are talking lives, lives and deaths and most of these are kids, just to me it doesn't make any sense."
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.