Bloomberg to be NRA's 'counterweight' in elections WASHINGTON, April 27 (UPI) -- New York Mayor Michael Bloomberg said he's tapping into his vast fortune to provide a political counterweight to the National Rifle Association. Bloomberg, long a gun-safety advocate, said senators of both parties who voted against expanding background checks earlier this month will face campaign advertisements slamming them for their vote, National Public Radio said Saturday. First up: Sen. Mark Pryor, D-Ark., who faces a tough battle for re-election in 2014. "This is just a toe in the water," said John Feinblatt, Bloomberg's chief policy adviser. The mayor and others are going to provide the political counterweight to the NRA. It has had the field to itself for decades, and that has to stop. And that time has come. Organizing for America, the grassroots policy advocacy group that grew out of President Barack Obama's campaign volunteer system, will also be turning up the heat on senators who balked on gun background checks. That group's leader, Jon Carson, told The Hill members were unafraid of targeting the four Senate Democrats -- all from red states -- who voted against the bill, even if it meant targeting members of the president's own party. "We're going to look to change votes on both the Democrat and the Republican side," he said. I disagree with that political calculus. I think it's very clear that even in those red states, there's overwhelming support for background checks. Bloomberg's group is also said to be targeting Republican Sen. Kelly Ayotte of New Hampshire. Her predecessor, Judd Nelson, another Republican, voted to extend the assault rifle ban. Ayotte voted against the background check amendment.