In the end, the Senate voted largely along party lines this week to kill even the most modest new gun-control measures. Efforts to place new regulations on firearms aren't likely to be resurrected in this Congress.
Mr. Bloomberg's organization, Mayors Against Illegal Guns, hired a team that included SKDKnickerbocker and Tom Synhorst of DCI Group, dividing the work by political party, in essence tapping each to do what they do best -- run ads taking aim at the other side.
SKDKnickerbocker, a public affairs and political consulting firm that works for Democratic candidates, targeted Republican Senators. Mr. Synhorst, a GOP political strategist with the DCI Group, focused on Democratic Senators.
The ads were produced by several firms, including the Lighthouse Group in Florida, which created the most recent ads, and Devine Mulvey, a Democratic media firm.
Mr. Bloomberg's most recent campaign -- a $12 million TV and video effort -- targeted the following Republican Senators: Jeff Flake of Arizona; Saxby Chamblis and Johnny Isakson of Georgia; Dan Coats of Indiana; Charles Grassley of Iowa; Susan Collins of Maine; Kelly Ayotte of New Hampshire; Lamar Alexander and Bob Corke of Tennessee; Dean Heller of Nevada; Rob Portman of Ohio; and Pat Toomey of Pennsylvania.
Some of the ads were generic, panning on paper angels created in Newtown to honor its slain children and asking voters to call their senators and urge them to support "comprehensive background checks on gun sales . . . that will protect the Second Amendment and help keep guns out of the hands of dangerous criminals. "
Other ads were more focused. The one that ran in Arizona, for instance, ran old interviews of Mr. Flake advocating stronger background checks.
In the end, only Ms. Collins and Mr. Toomey voted for the proposal that would broaden FBI background checks on prospective gun buyers. Facing a tough re-election next year and eager to win support from Pennsylvania's suburban voters, Mr. Toomey was expected to vote for the background check proposal because he crafted it with Democratic Sen. Joe Manchin of West Virginia.
Ms. Collins has been a long-time proponent of gun control, breaking with her party by voting for bans on assault weapons in the past, so the ads that ran in Maine were likely aimed at her rural constituents.
"Cleary the decision of Republicans [on the background-check vote] was a wet kiss to gun manufacturers and the National Rifle Association," said Doug Thornell, senior VP of SKDKnickerbocker. "All you can do is try to move public opinion on your side."
Democrats targeted by the ad campaign included: Mark Pryor of Arkansas; Joe Donnelly of Indiana; Mary Landrieu of Louisiana; Kay Hagan of North Carolina; and Heidi Heitkamp of North Dakota.
Of those, Mr. Donnelly, Ms. Hagan and Ms. Landrieu voted for the background-check measure.
Ms. Landrieu said her vote was not swayed by an ad called "Family" that featured a fatigue-clad hunter, sitting on the back of a pickup truck holding a shotgun who says he supports comprehensive background checks "so criminals and the dangerously mentally ill can't buy guns. That protects my rights, and my family."
Even though the Mayors Against Illegal Guns ad campaign could not break the stranglehold the National Rifle Association and other gun-rights advocates hold on members in Congress, polls indicate the multi-million dollar effort may have swayed voters. According to several surveys, large majorities, ranging from 86% to 92% of those polled, said they favored broader background checks.
But poll results can't compete with a passionate, motivated voter base quick to hit at something near and dear to politicians: job security.
The NRA countered the gun-control lobby with its traditional tactics -- by galvanizing its members with its trademark orange postcards and threatening lawmakers who voted against them with a poor NRA ratings opponents could use against them. The NRA ran some ads, but not nearly as many as its opponents. One, which ran on political news web sites on the day of the Senate vote, said the nation's police officers overwhelmingly oppose President Obama's gun-control agenda.
"President Obama and Mayor Bloomberg are pushing gun control," a narrator says. "But America's police say they're wrong."
Despite the setback, Mr. Bloomberg said he will continue his campaign and is likely to use his PAC to fund campaign ads next year.
The "vote was disappointing but we have still made historic progress on gun-violence prevention and we're in this fight for the long haul," said Mayors Against Illegal Guns spokeswoman Erika Soto-Lam