CHICAGO (AP) — A former Illinois legislator who favors an assault weapons ban captured the Democratic nomination Tuesday in the race to replace disgraced ex-U.S. Rep. Jesse Jackson Jr., after a campaign dominated by gun-control issues in the wake of the Connecticut elementary school massacre.

Ex-state Rep. Robin Kelly’s nomination all but assures that she’ll sail through the April 9 general election and head to Washington, because the heavily minority district is overwhelmingly Democratic. The Republican nominee was also being chosen Tuesday night.

The special primary election was the first race for a seat in the House of Representatives since the Dec. 14 mass shooting at Sandy Hook Elementary School in Newtown, Connecticut, left 20 children and six educators dead.

From a crowded field of candidates in the Chicago-area district, Kelly emerged early as a leader on gun-control issues. The former state representative from Matteson, a south Chicago suburb, favors an assault weapons ban, which is among the gun measures backed by Obama in response to school massacre.

During the campaign, New York City Mayor Michael Bloomberg’s super political action committee, Independence USA, poured more than $2 million into the race by airing anti-gun ads in Kelly’s favor and against another Democratic front runner, former U.S. Rep. Debbie Halvorson. Halvorson, who unsuccessfully challenged Jackson in a primary last year, is against such a ban.

Bloomberg has been leading an anti-gun campaign backed by Mayors Against Illegal Guns, a coalition he started that now has more than 800 mayors from around the U.S.

The result was a setback for the influential gun-rights lobbying group, the National Rifle Association, which gave its highest “A” rating to Halvorson and a failing “F” rating to Kelly.

After casting her ballot in the snowy weather that pelted the region Tuesday, Halvorson warned that if the ads were successful Bloomberg would try to “buy seats” across the country. “We can’t let that happen,” she said.

Guns were a leading issue at candidate forums and email blasts from candidates, even as Jackson’s legal saga played out in court and frustrated voters who’ve seen two other congressmen in the office leave under an ethical or legal cloud.

Jackson resigned in November, after a months-long medical leave for treatment of bipolar disorder and other issues, then pleaded guilty earlier this month to charges that accused him of misspending $750,000 in campaign money on lavish personal items, including a Rolex watch and fur coats.

Jackson’s exit created a rare opening in a district where he was first elected in 1995. The primary featured 14 Democrats, including former U.S. Rep. Mel Reynolds, who held the seat in the 1990s but served prison time after being convicted of fraud and for having sex with an underage campaign volunteer. There were four Republicans on the ballot.

Voters heading to the polls Tuesday indicated that guns, ethics and economic woes were on their minds.

Mary Jo Higgins of south suburban Steger said she voted for Halvorson because the former congresswoman is “the only Democrat who believes in the Second Amendment” of the U.S. Constitution, which guarantees the right to bear arms.

But Country Club Hills minister Rosemary Gage said she voted for Kelly because the former representative is “standing with (President Barack 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.”

Copyright 2013 The Associated Press.