There were more than 500 gun deaths in Chicago in the last year, and President Obama is scheduled to return to his hometown to discuss the issue on Friday.
Halvorson represented the more rural 11th District in Congress for one term, from 2009 to 2011, and in 2012 unsuccessfully challenged Jackson for the Democratic nomination in the redistricted 2nd District, which now includes more suburban areas.
On her campaign website, Halvorson argues an assault weapons ban in Chicago's Cook County has done little to curb gun violence.
"In Cook County, we have had an assault weapons ban in place for 20 years. However, Chicago still holds the negative distinction of having the highest number of murders in the United States, while not addressing the real concerns of mental health, background checks and straw purchases," she writes.
That's a huge buy in the district, especially considering most of the candidates in the race haven't raised enough to air any television ads at this point.
Bloomberg's super-PAC spent heavily in a number of 2012 races against candidates it deemed to be enemies of gun control, including Reps. Daniel Webster (R-Fla.) and Joe Baca (D-Calif.). Webster won reelection, but Baca was defeated.
Halvorson started off the crowded Democratic primary race with the highest name recognition of any of the 17 candidates. But the race could be turning more into a competition between former Cook County Administrator Robin Kelly (D) and Illinois state Sen. Toi Hutchinson (D).
The Chicago Tribune endorsed Kelly on Sunday, and both have done much better in securing local support and donations than Halvorson.
Reps. Danny Davis (D-Ill.) and Bobby Rush (D-Ill.) have both endorsed Kelly (D) — who has been running on the gun control issue — giving a potentially big boost to her campaign in the crowded field. Halvorson is the only white candidate.
Rush highlighted gun control as a reason for his endorsement of Kelly.
"Our communities are facing an epidemic of gun violence, and we need more members of Congress who can be trusted to fight for common sense gun control measures. Robin Kelly is a woman of integrity and conviction, and President Obama, Congressman Davis and I need her as our partner in ending gun violence," Rush said.
The primary is being held Feb. 26, and the special election is set for April 9.