Kelly, too, was among those criticizing Hutchinson's previous position and questioning whether her newfound stance was genuine. Now, Kelly says she's pleased to have her former rival's backing.
"In Congress, I will work with Sen. Hutchinson ... and other leaders throughout our district to get guns off our streets and bring jobs to our neighborhoods," Kelly said in a statement.
With Hutchinson's departure, the race is down to three top Democratic contenders: Kelly, Chicago Alderman Anthony Beale and Halvorson. The primary will likely decide the race because the district is so overwhelmingly Democratic.
Illinois' 2nd district also has a majority of black voters, even after boundaries were redrawn to include rural areas where there are greater numbers of white voters and where Halvorson is from.
Halvorson said Sunday that she believes she can easily woo those who had supported Hutchinson. She said in an interview that she was surprised by the sudden withdrawal and questioned what was behind the decision.
"There's no way that she would get out of the race unless she was told that she had no choice," Halvorson told The Associated Press. "And now what kind of deal was made? What is she going to get out of it? And I think everybody should come clean. ... This district is tired of wheeling and dealing."
Hutchinson's campaign did not respond to requests for comment.
Kelly told the AP that as far as she was aware there were no backroom negotiations or political deals made and that Hutchinson's decision was hers alone. She also does not think the ads by Bloomberg's PAC were any kind of tipping point in that decision.
Kelly defended the New York mayor's right to weigh in on an election in Illinois with ads endorsing her on the gun control issue and attacking her opponents.