Washington The $27 million poured into the 2014 U.S. Senate race in Louisiana by outside political groups contributed to the explosive growth in independent spending in campaigns nationwide, but fell well short of the amounts dumped into the costliest Senate elections, according to a report this week from a nonprofit organization.

Since the 2010 Citizens United decision by the U.S. Supreme Court removed limits on contributions to independent political groups, outside spending on Senate campaigns nationwide has more than doubled, to nearly $500 million last year, the Brennan Center for Justice reported.

“Citizens United definitely gave the green light to an explosion in outside spending,” Brennan report author Ian Vandewalker said Thursday.

The No. 1 target for outside groups in 2014 was the Senate race in North Carolina, with $80 million spent, the report said. Republican Thom Tillis defeated incumbent Democrat Kay Hagan in that election. The races in Colorado ($68 million) and Iowa ($59 million) ranked second and third.

In all three of those elections — as in Louisiana, where U.S. Rep. Bill Cassidy, of Baton Rouge, ousted incumbent Mary Landrieu — Republicans captured a seat previously in Democratic hands, contributing to the gain of nine seats that has given Republicans control of the Senate in the current Congress.

The outside spending in Louisiana reported to the Federal Election Commission ranks in the lower half of outside spending totals in 11 competitive Senate elections in 2014, according to the Brennan report.

The Brennan report doesn’t deal much with Louisiana because the report is based on spending through Nov. 4, when most states conducted their final votes but Louisiana held an open primary. The Louisiana race extended through a runoff Dec. 6; runoff spending is included in totals provided to the FEC.

The overall numbers understate outside spending in any case because they don’t include early campaign outlays by some groups on advertising that may attack or defend a candidate but does not specifically advocate for that candidate’s defeat or victory. Such spending is not included in FEC filings.

Outside spending to benefit Landrieu easily outpaced the amount helping Cassidy through Nov. 4, $10.5 million to $5.6 million, the Brennan center said. She finished first, just ahead of Cassidy, in the primary, but short of the majority needed for an outright win. The third-place finisher, tea party Republican Rob Maness, took most of the rest of the votes.

Polls widely predicted a Cassidy victory in the head-to-head Dec. 6 matchup, and outside spending for Landrieu dried up after Nov. 4. But outside groups spent another $10 million in the runoff to help Cassidy nail down the win, FEC filings show.

Spending by Louisiana Senate candidates from their own campaign committees, which are subject to limits on individual contributions, totaled $40 million in 2014, according to the FEC. That put the state in the clear minority among the 11 competitive races, the Brennan report said. In most of those cases, outside spending eclipsed candidate spending, the report said.

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