Minnesota legislative races, long low-dollar affairs, have exploded into six-figure contests, with campaign spending for House and Senate seats doubling over the past decade.

Examining data from every legislative race for that period, the Star Tribune found that candidates, parties and political action committees spent nearly $24 million on Minnesota’s House and Senate races in 2012. In 2002, that figure was less than $12 million.

Until 2012, only two legislative races — both in 2006 — had ever topped $500,000 in Minnesota for election spending. Last year, nine legislative races passed that milestone, while another 29 came in at more than $200,000.

In Minnesota and across the nation, legislative races are shattering all previous spending records as political groups pool their cash and bring their best data, staffing and technical resources to bear in statehouse districts.

Much of that is driven not by the candidates, but by political action committees and parties.

The choice for political interests is clear: They can spend millions on high-stakes congressional races, win a few seats and still see Congress mired in gridlock. Spend those millions on legislative contests, and they can get quick change and massive state-by-state results.

Partly because of this shift in strategy, more state Capitols are controlled by a single party than at any time in modern history.

“You can take that same amount of money and you can, literally, as we saw here in Minnesota, flip entire legislatures in one election cycle,” said Keith Downey, chairman of the Minnesota Republican Party.

Downey is a living example of what can happen.

A two-term House member, Downey decided to try for the state Senate in 2012. His race against first-time DFL candidate Melisa Franzen became the most expensive legislative race in state history, totaling $870,000. Downey and Franzen each spent a little over $110,000. But outside groups turned the contest — in which 50,000 votes were cast — into a monster race. Independent expenditures to defeat Downey ran more than $300,000 — nearly twice what interest groups spent against Franzen.

After he lost, Downey took over as head of the state GOP.

As the two parties fight for control of the House and Senate, the stakes have risen in every district with the potential to swing to the other side.

A House race that cost, on average, $50,000 in 2002 now costs $91,000, with many seeing far more spending. By last year, spending for the average Senate seat topped $171,000, up from $78,000 a decade ago, for an increase of more than 100 percent.

The 2012 legislative election marked the first time that independent spending by outside groups — parties and political action committees — outstripped spending by the men and women on the ballot, according to the Star Tribune analysis of state campaign finance reports.

Like drowning

Evidence of the changing nature of legislative races hit first-time candidate Zach Dorholt late last year, as the St. Cloud DFLer prepared to “zombie out” after a long day of campaigning by watching a cable showing of the science fiction movie “Predator.”

Suddenly, an attack ad blared out from his TV. About him.

“I never in my life expected to see not only TV ads for or against a House candidate but for myself,” said Dorholt. He toppled Republican Rep. King Banaian last year in what became the state’s most expensive House race.

But that wasn’t because of Dorholt. The 32-year-old marriage and family counselor spent a total of $26,000 on his race, compared with $40,000 spent by Banaian. Interest groups flooded the race with another $488,000.

“I’ve never experienced drowning before, but that’s a little what it felt like,” said Banaian, a professor of economics at St. Cloud State University.

Preparing for battle in 2014

Next year may get even more explosive. Republicans are desperate to break the Democrats’ top-to-bottom control of state government, which includes the governor’s office, both chambers of the Legislature and every constitutional office. DFLers are just as eager to turn their short-term victory into a more permanent majority. Political interests also are preparing for battle.

In a series of private meetings, Republicans and some business interests are talking about pooling their resources as never before, to turn their Capitol goals into electoral reality. Calling their past efforts haphazard and using DFLers as a model, they have vowed to unify.

“I think it’s important to get things done because the election isn’t that far off,” Stanley Hubbard, chairman of Hubbard Broadcasting, Inc., said this summer. Hubbard has long been a major GOP donor in Minnesota.

But DFLers are not sitting back.

“The members of the organizations that we represent remember the disaster of the 2011-12 legislative session and the victories for working families in 2013,” said Carrie Lucking, executive director of the Alliance for a Better Minnesota, referring to the period when Republicans controlled both the House and Senate. “They will have a strong interest in maintaining middle-class majorities.”

Fueled by cash from unions and wealthy Minnesotans, the Alliance poured nearly $2 million into independent expenditures in targeted legislative races last year.

Only the DFL Party, with $3.5 million in independent spending on legislative races, spent more in 2012.

Legislators, stunned at the level of outside money pouring into their races, are working to take back their races.

In the waning hours of this year’s legislative session, Gov. Mark Dayton and a bipartisan majority of legislators approved higher spending and contribution limits for Minnesota candidates — the first increase in more than a decade.

Those new limits raise the amount individuals can give to House candidates by nearly 70 percent. House candidates now can also spend $60,000 — up from $41,000 — and still get campaign subsidies. Similar increases were approved for other candidates as well.

“This is a direct reaction to the large amounts of money that are being spent by third parties in elections that leave candidates, very often, without the ability to have very much of a voice in their own elections,” Rep. Ryan Winkler, DFL-Golden Valley, said during debate on the issue.

The effect of PACs

Ten years ago, parties and political action committees (PACs) sought influence by donating money directly to the candidates, giving those on the ballot power over how the money was spent.

Now those groups spend the cash themselves, giving them tight control over the tone and timing of political messages.

In the Dorholt-Banaian contest, the race to represent a district of fewer than 40,000 residents and 81 square miles drew money from labor groups, the DFL Party, the national super PAC Progressive Kick, the state House Republican Campaign Committee, the pro-Republican Minnesota’s Future and other assorted business and liberal interests.

In that race, groups trying to get Dorholt elected spent about $300,000 and those rooting for Banaian spent about $200,000.

Republican interests were outgunned that year not just in that district, but in most other competitive races.

The Star Tribune’s analysis showed that Democratic interests outspent Republican groups in 25 of the 40 most expensive contests. In those races, Democratic groups spent $6.9 million — 20 percent more than the $5.8 million mustered by Republican groups.

While money is not the only determining factor, DFLers swept to victory in 32 of those races, with Republicans winning eight.