A torrent of third-party spending has produced a drastic spike in the amount of negative advertising during the 2012 presidential election, a new study finds.

An analysis by the Wesleyan Media Project found that 70 percent of advertisements so far have been negative, meaning they mentioned an opponent rather than touting a candidates' platform or qualifications. That is a huge increase over 2008, when negative ads comprised a mere 9 percent of the total.

An influx of outside spending has fundamentally reshaped the process. The Supreme Court's 2010 Citizens United decision, combined with a lower court ruling, opened the floodgates by lifting spending restrictions and giving rise to entities called Super PACs that can raise and spend unlimited amounts of money. Although Super PACs are barred from coordinating with candidates, every prominent candidate has had an allied Super PAC that launches advertisements and direct mailings on the candidate's behalf.

The result has been an outsize role for interest groups and Super PACs. In 2008, spending by candidates accounted for about 97 percent of ad buys, with interest groups making up the rest. So far in 2012, interest groups have purchased some 60 percent of the ads run so far, compared to about 36 percent sponsored by candidates.

Such levels of outside group involvement in a presidential primary campaign are unprecedented, Travis Ridout, co-director of the Wesleyan Media Project, said in a posting accompanying the study. This is truly historic. To see 60 percent of all ads in the race to-date sponsored by non-candidates is eye-popping.

The overall tenor of advertisements has flipped. In 2008, a little more than 8 percent of candidate-sponsored ads were negative and negative ads made up about 25 percent ads paid for by interest groups. In 2012, a majority -- 53 percent -- of candidate-sponsored ads have been negative, while a whopping 86 percent of those purchased by interest groups have attacked other candidates.

Crossroads GPS, an arm of the American Crossroads Super PAC that was founded by top Republican strategist Karl Rove, has easily outpaced other interest groups so far by spending some $12.6 million. Other leading interest group ad spenders have included the conservative Americans for Prosperity ($6.9 million), the American Energy Alliance ($3.3 million) and the fiscally conservative American Future fund ($2.9 million). All three are organized in such a way that they are not required to disclose their donors.

Super PACs also bankrolled the advertising assaults of several presidential candidates. Jon Huntsman, Newt Gingrich, Rick Santorum and Mitt Romney all had the majority of their advertisements paid for by sympathetic Super PACs, underscoring a campaign dynamic in which Santorum and Gingrich relied on outsider ad buys -- in Gingrich's case, funded largely by the billionaire Sheldon Adelson -- to fend off a barrage of negative ads from Romney's deep-pocketed allies. 

Over an eleven-day period in mid-April, Crossroads GPS sponsored more advertisements in media markets across the country than the Obama campaign and its supporting Priorities USA Action Super PAC combined. But that balance could change as the general election gets underway: in a reversal that contradicted Obama's vocal criticism of the Citizens United decision, the Obama campaign began urging donors to contribute to Priorities USA in an effort to counteract Republican Super PAC spending.