Outside spending more than doubled in the 2014 Senate elections compared to the 2010 midterm equivalents, according to a new report.

The Brennan Center for Justice estimated that $486 million was spent by outside groups in the most recent Senate elections. In 2010, Senate races drew $220 million in outside spending, adjusting for inflation. Of the total 2014 sum, less than $50 million was spent on the 22 non-competitive races combined.

North Carolina’s race — between incumbent Sen. Kay HaganKay Ruthven HaganNC state senator meets with DSCC as Dems eye challenge to Tillis GOP, Dems locked in fight over North Carolina fraud probe 2020 Dems compete for top campaign operatives MORE (D) and Thom TillisThomas (Thom) Roland TillisDems ready aggressive response to Trump emergency order, as GOP splinters Business, conservative groups slam Trump’s national emergency declaration GOP senator dedicates heart photo to wife from Senate floor for Valentine's Day MORE (R) — attracted the most outside money by far, with groups spending $80 million. In the end, Tillis ousted Hagan.

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The estimates are based on Federal Election Commission data, which the group behind the report said is incomplete because it does not include spending on “issue ads” that do not need to be declared.

The report’s authors also found that outside groups continue to grow in influence and spending power. The groups’ expenditures made up 47 percent of the total spending in Senate races, while candidates’ accounted for 41 percent of spending.

There were exceptions to that rule. Races in Georgia, New Hampshire and Kentucky each saw candidates outspending outside groups.

The assessment, which attempts to illuminate the campaign finance landscape in the aftermath of the 2010 Supreme Court decision in Citizens United v. FEC, also strengthens one of the claims made by campaign finance reformers: Super-PACs are largely funded by a small core of wealthy individuals.

Sixty percent of money given to super-PACs in the 2014 cycle was donated by only 195 individuals and their spouses, the report says. More broadly, the hundred biggest donors during the midterms almost matched the aggregate contributions of more than 4 million small-amount donors.

In the Citizens United case, the court opened the door to unlimited corporate contributions to election ad campaigns — significantly expanding the financial scope of many political contests.