Gun control supporter Robin Kelly (D) cruised to victory over former Rep. Debbie Halvorson (D-Ill.), who favors gun rights, on Tuesday in the Democratic primary to replace former Rep. Jesse Jackson Jr. (D-Ill.), giving supporters of new gun-control laws a big win in Illinois at a key moment in their battle.

Kelly led Halvorson 56 percent to 20 percent with 60 percent of precincts reporting. Halvorson has called Kelly to concede the race.

A Halvorson win would have dealt a major blow to advocates of increased gun regulations Early on, a crowded field and Halvorson's high name identification in the district made that appear possible. But a combination of heavy spending against Halvorson, efforts by top Democrats to clear the field for Kelly and Halvorson’s own inability to raise any money or run much of a campaign led to her defeat.

Kelly, a former Cook County administrator who started out with little name recognition in the race, was aided greatly by more than $2 million in spending against Halvorson by New York City Mayor Michael Bloomberg’s (I) super-PAC. She also had help from many in Chicago’s Democratic establishment, including some close allies of President Obama.

Kelly's primary win all but guarantees her a spot in Congress in the heavily Democratic 2nd District.

In her victory speech, Kelly said voters sent a message that tells the National Rifle Association (NRA) "that their days of holding our country hostage are coming to an end. And their days of scaring Congress into submission on gun control are coming to a close."

The seat was left open when Jackson resigned late last year due to serious legal and ethics problems. He has since pleaded guilty to using hundreds of thousands of dollars in campaign funds for personal use, and is likely headed to jail.

Gun control advocates were quick to claim a win — and argued that gun control can be a salient issue nationwide.

"This is an important victory for common sense leadership on gun violence, a problem that plagues the whole nation. And it's the latest sign that voters across the country are demanding change from their representatives in Washington — not business as usual,” Bloomberg said in a statement released by his super-PAC, Independence USA. “As Congress considers the President's gun package, voters in Illinois have sent a clear message: we need common sense gun legislation now. Now it's up to Washington to act."

The big spending by Bloomberg — and efforts by some other Democratic super-PACs including CREDO — show that the NRA no longer is the only deep-pocketed organization focused on the issue. While Bloomberg’s group claimed some wins in 2012, this is first time since the Newtown, Conn., shootings put gun control in the national spotlight that it has been tested at the ballot box.

Bloomberg outspent all of the candidates — combined — leaving a big mark on the race. Another big factor: Chicago’s Democratic establishment also rallied hard to support Kelly, whose campaign chairwoman, Cheryl Whitaker, is a close friend of the Obamas.

Chicago’s two African-American congressmen, Democratic Reps. Danny Davis and Bobby Rush, endorsed Kelly. She also had the backing of Rep. Jan Schakowsky (D-Ill.), who is close to both Obama and House Minority Leader Nancy Pelosi (D-Calif.), and Chicago Mayor Rahm Emanuel worked quietly behind the scenes to clear the field and stop Halvorson, according to sources.

That institutional support for Kelly helped convince a number of other African-American politicians to drop out of the race, including Illinois state Sen. Toi Hutchinson (D), who then threw her support to Kelly. Hutchinson’s decision all but guaranteed a win for Kelly in the race.

Halvorson, the only white candidate in this election, was endorsed by the NRA in her losing 2010 reelection bid. She ran against Jackson in the 2012 Democratic primary and held to 29 percent of the vote then — a mark she appears to have failed to reach in this election.

The election comes at a key time in the debate over gun control. The Senate is set to begin marking up new legislation later in the week, and its prospects appear uncertain — especially a renewed ban on assault weapons that Obama supports.

While a Democratic primary in a heavily African-American Chicago-based district that has been racked by gun control isn’t the best barometer of the national mood, the margin of Kelly’s victory could be a warning to Democrats who oppose new gun control measures — and possibly some suburban Republicans as well.

--This report was updated at 10:53 p.m.