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Groups spent at least $15 million last year trying to influence Minnesota state elections through so-called "independent expenditures," which is in addition to money spent by individual candidates, according to the latest filing from the Minnesota Campaign Finance and Public Disclosure Board.

DFL-aligned groups outspent their Republican counterparts considerably, by $10 million to $6 million.

In addition to nearly $2.9 million by the state party and more than $900,000 by the DFL House caucus, Democrats were helped by familiar names: The Alliance for a Better Minnesota Action Fund spent more than $4.5 million. Big labor unions PACs also pitched in, including Education Minnesota with more than $400,000 and big totals from AFSCME, SEIU and the nurses union.

On the Republican side, the party pitched in with $1.3 million. Minnesota Action Network, with which former Sen. Norm Coleman is affiliated, spent $657,000; Pro Jobs Majority spent more than $1 million, with several similar, business-backed groups chipping in six figure chunks. The House Republican caucus spent $440,000.

What's not known, however, is how much was spent by so-called "dark money" groups, nonprofit groups that can spend unlimited, concealed sums on elections and have sprouted up since the U.S. Supreme Court began deregulating campaign spending via the Citizens United decision. Republicans are believed to be the bigger beneficiary of this spending.