Against the backdrop of a city plagued by violence, the nation’s renewed debate over guns has taken center stage in a Chicago-area congressional race. The campaign is a test of whether gun-control advocates led by one of the nation’s leading activists can defeat former congresswoman Debbie Halvorson, arguably the front-runner for Jesse Jackson Jr.’s old seat.

In this March 20, 2012 file photo, Democrat Debbie Halvorson speaks to supporters as she gives her concession speech in Homewood, Ill., after losing her primary election to U.S. Rep. Jesse Jackson Jr. in Illinois’s 2nd Congressional District. (Seth Perlman — Associated Press, File) (Seth Perlman -- AP)

New York City Mayor Michael Bloomberg, one of the country’s most vocal advocates of gun control, is putting his political muscle behind an effort to ensure that Halvorson, a Democrat and the recipient of an “A” rating from the National Rifle Association, does not win.

His super PAC recently unleashed a rough attack ad against the congresswoman citing the high mark she previously received from the NRA, and declaring: “When it comes to preventing gun violence, she gets an F.” The super PAC has reportedly put nearly $700,000 behind the spot.

Halvorson, who says she is not pursuing the NRA's endorsement in this race, contends the attacks haven't worked. If anything, she argues, they are galvanizing her supporters.

“So far, from what I have seen, it is not hurting my chances at all,” Halvorson told The Fix in an interview. She said voters have expressed anger that a “billionaire from New York is trying to come into Illinois and buy an election.”

At least one other candidate would disagree. On Wednesday, former state representative Robin Kelly released a poll showing her with slight leads on Halvorson and state Sen. Toi Hutchinson, who has reversed her position on gun control. Kelly’s pollster attributed her momentum to the debate over guns. "This is what this race is about," he told The Hotline.

Kelly has been underscoring her support for stricter gun-control measures and favors a ban on assault-style weapons, something Democratic lawmakers have introduced on Capitol Hill and President Obama supports. She launched a five-figure cable TV buy on Thursday for a spot touting her position on guns.

Halvorson said she doesn't support a federal assault weapons ban, but favors requiring universal background checks for gun purchases. She said that her support or opposition to a ban on high-capacity ammunition magazines would depend on the specifics of the proposal.

For her part, Hutchinson formerly opposed a ban on assault-style weapons, but has reversed her position, the Chicago Tribune reported this week. She said her views about the NRA have changed in the wake of the mass shooting at Sandy Hook Elementary School in Connecticut.

The competitive race is unfolding in a city that has faced a mounting problem with violence. There were more than 40 murders in Chicago last month, the deadliest in the city in more than a decade. Chicago hit the 500-homicide mark last year for the first time since 2008.

Halvorson is one of more than 20 candidates running to represent Illinois’s 2nd District, which includes Chicago’s South Side and extends southward into the suburbs. For several reasons, she can lay claim to the mantle of front-runner.

For one thing, she enjoys a name recognition advantage, by virtue of her stint in Congress. Starting in 2009, Halvorson spent one term as the 11th District congresswoman, during which time she represented many suburban voters who now reside in the 2nd District, following the decennial redistricting process. Her campaign estimates that more of 50 percent of the current district  is territory Halvorson previously represented.

Halvorson is also the most prominent white candidate in a field with African-American contenders who could split the black vote, which could pave the way for her to win with plurality support. Hutchinson and Kelly are African American.

The Democratic primary, which is really the de facto general election, given the district’s strong Democratic tilt, is Feb. 26. Moving ahead, the extent to which Bloomberg’s organization will remain in the race and how voters will respond to the advertisements from his group are two of the most important questions to be answered. Thus far, there’s been an apparent dearth of public polling in the contest.

Halvorson contends the main issue in the campaign is the economy. But at this point, it's plain to see that the debate over guns is a major issue driving the contest.