About $97 million was spent by outside groups on media buys categorized as primary spending for the mid-term elections, according to Sunlight Foundation analysis of Federal Election Commission data. Of the $95 million in spending where a party identification could be determined, Republican-leading groups outspent Democrats $59 million to $36 million.

But Democrats were the big spenders on attack ads, which Sunlight suggests is an effort to soften up the candidates for November, so general election-targeted spending classified as primary spending.

The top spender on ads and related ad production and ad buyer expenses was the Senate Majority PAC at $13,021,696, with all but about $2 million of that spent on ads opposing Republicans.

The U.S. Chamber of Commerce spent $11,580,732 at number two, with almost $10 million of that supporting Republicans, another $762,5000 spent opposing Democrats, and $1 million opposing Republicans.

Club for Growth Action was at number three, spending $6,240,774, with $4,678,119 spent opposing Republicans.

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