Illinois state Sen. Toi Hutchinson dropped out of the race and endorsed rival Democrat Robin Kelly, a former state representative who is now a Cook County official.
The Democratic primary election to fill Jackson's former seat will take place on Feb. 26.
Kelly faces former Rep. Debbie Halvorson (D-Ill.) in the upcoming primary. Halvorson on Sunday accused Hutchinson and Kelly of striking a backroom deal.
“With nine days remaining in this primary, a behind the scenes closed door meeting was struck between Toi Hutchinson and Robin Kelly. The voters of the 2nd Congressional District deserve better,” she said in a statement.
“These old political games are what got us in this mess in the first place,” she added.
Gun control had emerged as a central issue in the race, with New York Mayor Michael Bloomberg’s (I) super-PAC and CREDO super-PAC, a liberal group, both targeting Hutchinson and Halvorson over their strong ratings from the National Rifle Association.
"The NRA would like members of Congress to believe that politicians who vote for sensible gun regulations will pay the ultimate price come election time," said Becky Bond, President of CREDO super-PAC in a statement. "But we're proving in this race that it's the politicians who do the NRA's bidding who will be in trouble when they face the voters. If you are with the NRA -- Democrats included -- there is an army of activists ready to help defeat you in your next election."
Jackson resigned his seat after winning reelection in November. On Friday he was charged in federal court with crimes relating to the misuse of $750,000 in campaign funds. Jackson, who will plead guilty to the charge, allegedly used the money to fund a lavish lifestyle replete with a $43,000 Rolex watch and multiple items of Michael Jackson clothing.
This post was updated at 4:26 p.m.