The report found that of the $189 million spent as of Oct. 23, nearly half of that money has been concentrated on the intensely competitive Senate races in Virginia, Ohio, Wisconsin and Nevada. Notably, the expenditures also reflect a recent shift towards independent groups and away from the traditional party hierarchy.
Several media reports have focused on the profusion of outside spending in the 2012 presidential race, but Citizens United-enabled donations from super PACs and non-party organizations have also poured into the down-ticket races for the House of Representatives and the Senate.
"It's clear that there is a lot more outside money than there would have been had the [Supreme] Court not ruled as it did in Citizens United," study author Lee Drutman told The Huffington Post. "The further down ballot you get, the more important each individual dollar is and the more access it can potentially buy."
Unlike in the presidential contest, neither party enjoys a whopping cash advantage in Senate race expenditures: Republicans edged out Democratic spending by only $5 million, having distributed $97.3 million by Oct. 23 compared to the Democrats $92.1 million.
But what proved most interesting, Drutman said, is the extent to which non-party and non-super PAC groups have coughed up cash.
"The Republican Senate Committee has been eclipsed by Crossroads GPS and the Chamber of Commerce," Drutman said. "And it's interesting that the power structure of the Republican Party has also moved away from the traditional party structure and that Karl Rove and the Chamber have taken on the role of kingmakers now. One of the things that we are looking at now is to see just how closely are the giving patterns of these groups aligned."
Thus far this cycle, the GOP committee, at $17 million, provided just 17.5 percent of the money spent to support their candidates. Crossroads GPS and the Chamber have each donated $25 million and $20 million, respectively.
However, the Democratic Senate Campaign Committee still remains the number one group in Senate contributions, divvying out more than $33 million.
Donations to party committees are capped at $30,800 per individual or corporation, which could explain why outside groups have seen their coffers swell after the Citizens United decision allowed for unlimited giving to unaffiliated groups.
But Drutman speculates that, for donors, much of the appeal of 501(c) organizations like Crossroads GPS and the Chamber lies in their anonymity. Under Federal Election Commission laws, these organizations do not have to disclose their donors. Nor do they have to reveal where and how they spend their money, except during the 60 days immediately prior to an election.
Super PACS, on the other hand, must reveal both their donors and their expenditures.
"Crossroads GPS has spent four times what [its affiliated super PAC] American Crossroads has spent," Drutman said. "And that's just within the 60-day window; beyond the 60-day window, they don't have to tell you anything. So we know they spent a lot more."
He adds, "The pitch from Crossroads GPS to donors is that they can guarantee you anonymity. And there are a lot of donors who want that."
Drutman points to the vehement backlash that Target faced from its consumers after the corporation gave $150,000 in support of an anti-gay Republican running for governor in Minnesota in 2010.
"Especially consumer-facing companies are nervous that they would upset the politically minded consumers of their products if those consumers learned about their political activities," he said. "At the same time, there are outcomes in Washington that they care very much about, so they would like to influence those outcomes."
In fact, one of the founders behind the Crossroads operations, Carl Forti, pointed to the nondisclosure rules as the impetus behind forming a 501(c) group in the first place.
"Disclosure was very important to use, which is why the 527 [American Crossroads] was created," Forti told Politico in 2010. "But some donors didn't want to be disclosed, and therefore, a (c)4 [Crossroads GPS] was created."
The U.S. Chamber of Commerce, the second heavyweight supporting GOP Senate candidates, has actively fought initiatives that would require it disclose its donors.
Over the summer, the White House contemplated issuing an executive order that would require all government contractors to disclose their political spending -- a measure that would primarily affect big businesses. The Chamber led a pressure campaign to successfully stall the issue, said Robert Weissman, executive director of the Washington-based accountability group, Public Citizen.
"The Chamber is the primary conduit for all of this corporate money coming into campaigns," Weissman said at an Oct. 19 press event held in opposition to the Chamber's practices. "The Chamber has its own institutional interest in soliciting, obtaining and spending these contributions. The Chamber's base of power to a considerable extent depends on being able to maintain the secrecy around campaign spending."
The pro-business association -- which has drawn fire for doing more to support large corporations even as it touts itself as a small business representative -- has pledged to spend at least $100 million in total during the 2012 election, according to a new Public Citizen report.
For Melanie Collins, a Maine resident who runs a home child care business, says small businesses have a hard time keeping up with such massive amounts of political spending.
"Back home in Maine, the Chamber is by far the largest out-of-state spender in our Senate race," she said at Friday's event. "They just bought $500,000 of attack ads to elect a guy who promises to give the biggest tax break to the richest of us ... [Small businesses] certainly don't have millions of dollars to compete with them, even though together we employ the majority of the state."
The Chamber's attack ads are agitating more Maine residents than just Collins.
"You are criticizing one of our candidates," Dana Connors, the state chamber of commerce president, recalled telling a U.S. Chamber representative. "I'm concerned about that because it puts us into a political position that carries a negative [tone]. We're a state chamber. We live in the state every day. We're concerned about our brand."
As of Sept. 30, the U.S. Chamber has spent close to $1.4 million in Maine to oppose Senate candidate and former Gov. Angus King (I), according to the Sunlight Foundation.
Although there is a growing trend of donors funnelling money through 501(c) organizations, super PACs still make up close to one third of outside spending on Senate races. Democratic super PACs spent more than $33 million prior to Oct. 23, compared to $24 million from Republican-leaning super PACs.
While super PACs are forced to disclose their donors, a new report from Public Citizen calls into question just how "independent" many of these groups actually are from the candidates they support. More than half of the super PACs registered this cycle focus on a single candidate and they are often run by a family member, friend or close associate.
The group looked at all of the super PACs who have spent more than $100,000 in this election cycle; out of those 108 groups, 65 had dedicated themselves to electing only one person and had contributed a total of $203 million by mid-October, the report states.
"Single-candidate super PACs are making a mockery of the campaign finance system," report author Taylor Lincoln said in a press release. "Donors seeking to dodge contribution limits can simply give unlimited amounts to the candidate's super PAC."