Outside spending benefiting Obama over the same period never exceeded $14 million, records show.

Super PACs have raised about $660 million in the 2012 election.

Restore Our Future alone accounted for about $1 out of every $5 in super PAC donations received. The pro-Romney group raised more than $130 million, much of which was spent decimating the candidate’s rivals during the Republican primary.

The Obama-backing Priorities USA Action raised $64 million.

The amounts have grown significantly: In 2010, their first year of existence, all super PACs combined raised $85 million.

The explosion in outside spending has coarsened the political debate, flooding the airwaves in Ohio, Florida, Virginia and other battleground states with negative, often inaccurate ads.

Roughly 80 percent of all spending by conservative groups and liberal groups has been negative, FEC records indicate.

All of the nearly $57 million that Priorities USA Action reported spending has been on negative ads about Romney. The group, which coined the slogan “If Mitt Romney wins, the middle class loses,” linked him to the death of a woman who lost her battle with cancer.

Another of the super PAC’s most memorable ads featured a worker describing how building the stage on which officials announced his plant’s closure, after it was bought by Bain Capital, which Romney helped found, was like building his own coffin and it made him “sick.”

Eighty-eight percent of Restore Our Future’s spending went toward negative ads, as did 95 percent of the expenditures of American Crossroads, another super PAC.

Many of these ads have criticized Obama’s handling of the economy, arguing that the country “can’t afford” four more years of the president’s policies. One spot features a small-business owner saying, “We can’t create more jobs until Obama loses his.”

Others ads have featured disillusioned Obama supporters from 2008 expressing disappointment with the president.

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