Updated 4:24 p.m. ET

The millions that New York Mayor Michael Bloomberg spent in hopes of defeating a pro-gun Democrat in Chicago today may be just the beginning of a political spending spree prompted by a massacre of 26 students and teachers.

Voters in Illinois' 2nd Congressional District are the first to head to the polls in a federal election since a gunman went on a rampage at the Sandy Hook elementary school in Newtown, Conn., and they have gotten an early taste of the air wars that appear likely to dominate next year's races. A super PAC that Bloomberg created to advance a series of pet issues, including gun control, has spent $2.2 million opposing former Debbie Halvorson, a former one-term House member who is attempting a comeback in the Democratic primary  for the seat vacated by Jesse Jackson Jr.

Bloomberg's Independence USA PAC spent $1.3 million opposing Halvorson and $829,000 supporting her opponent Robin Kelly. Both candidates are Democrats in a district that is so heavily Democratic that today's balloting is considered tantamount to victory in the March 19 special election.

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• To see all of Sunlight's coverage, head to the Sunlight Foundation's resource page

The spending in the Chicago race appears to be a harbinger of things to come. The gun debate is heating up in Congress, with Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., setting a Thursday meeting of his panel to begin moving a package of gun control legislation towards the Senate floor. And the gun debate is already emerging as an issue for the 2014 election cycle. 

In the weeks since the State of the Union address, which President Barack Obama used to make an emotional appeal for gun control, at least seven groups have either purchased airtime in major markets around the country or posted TV-ready ads to their Youtube accounts. The groups run the political gamut from the National Rifle Association to Americans for Responsible Solutions, a super PAC started in response to Newtown by former Rep. Gabrielle Giffords, D-Ariz., herself a victim of gun violence.

Some of the ads are geared towards a national market with a generic pro- or anti- gun control message, while others are targeting specific members of Congress.

Mayors Against Illegal Guns, a nonprofit group that does not have to disclose the source of its funding is is co-chaired by Bloomberg, just made a move to buy ad time against one of the major Sunday morning talk shows in Washington. While the paperwork filed with ABC affiliate WJLA TV does not indicate the nature of the ad, the mayors group has just released this new one on its website.

Obama's own organization, Organizing for Action, a 501(c)4 group that grew out of his campaign organization, said last week it would spend up to $100,000 to target a dozen members of Congress with online ads for failing to support gun control measures. These include Republican Sen. Susan Collins of Maine, a member of her party's moderate wing. The Obama group has come under criticism because it is not required to disclose its contributors; it is reportedly seeking to raise $50 million and claims it will make public the identities of large donors.

The Progressive Change Campaign Committee, a pro-gun control group, is running a series of ads in Kentucky against Senate Republican Leader Mitch McConnell, who is up for reelection next year. The ads criticize McConnell's opposition to gun control.

MoveOn.org is running ads supporting gun rights reform and criticizing Republican Sen. Rob Portman of Ohio for taking money from NRA. Portman, a potential 2016 Republican presidential contender, initially suggested he'd be open to considering an assault weapons ban but later backed off.

"Portman needs to understand that it's not enough to pay lip service to gun violence prevention laws—his constituents need him to stand up to the NRA," said Garlin Gilchrist, the National Campaign Director at Moveon.org. "If he did so, it could send a strong message to other elected officials – and help us really move forward on passing meaningful legislation to reduce gun violence."

Meanwhile the NRA has posted a series of TV-ready ads to its website critical of universal background checks, gun registration proposals, and Obama. The group also said it is running newspaper ads in Arkansas, Louisiana, Maine, North Carolina, and West Virginia, attacking Obama's gun control proposals. CNN reported the total cost would be about $350,000.

The NRA did not return Sunlight’s calls requesting information on whether the ads have begun to air.

It's hard to know exactly how much money has been spent so far. At this point, only the ads in the Illinois special election are required to be reported to the Federal Election Commission. Ads that do not explicitly call for a vote for or against a candidate — such as the ones in Kentucky — to not have to be reported to the FEC until much closer to Election Day. Two databases maintained by the Sunlight Foundation, Ad Hawk and Political Ad Sleuth capture some, but not all, of the early political advertisements. A chart of some of the made-for-TV gun ads we've found is below. Know of any we are missing? Use the Ad Hawk mobile app to alert us or email us here.

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