The Democrat-turned-Republican-turned-independent has long taken a vocal stance against guns. He launched his super PAC weeks before the November election and spent more than $12 million to back seven candidates nationwide, including for newly elected Rep. Gloria Negrete McLeod, a California Democrat who ousted an incumbent during a race where guns were an issue.
On Tuesday, Kelly told supporters that she would work with Obama and Chicago Mayor Rahm Emanuel to get gun legislation through Congress.
However, gun rights advocates dismissed the notion that Kelly's election and Bloomberg's attention would fuel the debate on gun control.
"This is an aberration," said Illinois State Rifle Association spokesman Richard Pearson. "This shows what you can do with $2 million in an off season race. He bought the election is the way."
Another Democratic front runner, Chicago Alderman Anthony Beale, also took issue with the ads, saying people were "extremely upset" that someone from New York was trying to tell people in Illinois how to vote.
"That's what money gets you," he told the AP after conceding late Tuesday. "We earned every vote."
Roughly 14 percent of registered voters came to the polls, an estimate Chicago officials said was the lowest turnout in decades. Adding to the problem was a blast of wintry weather Tuesday that snarled traffic, cancelled hundreds of flights and could have kept some voters home.
But those who did make it out indicated that guns, ethics and economic woes were on their minds.
Mary Jo Higgins of Steger, a south Chicago suburb, said she voted for Halvorson because the former congresswoman was "the only Democrat who believes in the Second Amendment."
But Country Club Hills minister Rosemary Gage said she voted for Kelly because she was "standing with (Obama) and trying to get rid of guns."
"It's really bad in Chicago and across the country," Gage said. "Too many children have died."
Associated Press writer Sara Burnett contributed to this report.
Sophia Tareen can be reached at http://twitter.com/sophiatareen.