Minnesota's congressional candidates spent nearly $32 million on what are now the most expensive U.S. House races in state history.

Of those, U.S. Rep. Michele Bachmann accounts for almost half that total. The Republican firebrand tapped her nationwide donor base to unleash more than $15 million on the contest -- nearly as much as every other state congressional candidate combined.

The former presidential candidate is one of the House's most prolific fundraisers, raising more than $16 million for this year's congressional campaign. Combined with the $2 million raised by her Democratic challenger, hotel magnate Jim Graves, that makes the race for Minnesota's Sixth Congressional District one of the most expensive House races in the country.

The fourth-term Republican is accustomed to taking the top spending spot. According to the Center for Responsive Politics, her 2010 race was also the nation's costliest and her 2008 race ranked in the top 10.

"Her presidential campaign elevated her to the national platform and greatly increased her ability to raise funds," said Sheila Krumholz, executive director of the Center for Responsive Politics. Krumholz said that while Bachmann raised 30 percent of itemized individual donations from outside Minnesota in 2008, that figure grew to 86 percent in 2012.

A lightning rod for national Republican attention, Bachmann sent out appeal after appeal to win small-dollar donations in the final weeks of the campaign.

"Fellow Conservative, this is the toughest re-election campaign I have ever faced," she wrote to her massive list of supporters last month. "Your support has never been more important. I need your help to fight back."

She was right about the difficulty she would face. Bachmann beat Graves by only about 4,000 votes, which works out to about $80 spent per vote she received.

But her appeals for cash worked. According to federal filings, she raised $2 million between mid-October and the end of November. During that period she spent about $3 million.

Although many of Bachmann's requests focused on her bid for re-election, she also managed to find cash in her campaign to backfill her lagging presidential coffers with the donations that flowed in. Since late October, she has transferred more than $500,000 of her congressional cash to her presidential campaign to help retire some of the debt from her bid for the White House. She had previously moved more than $260,000 from her congressional campaign to her presidential effort.

She still owes vendors about $170,000 but she will start her next campaign with about $2.2 million left in the bank. Bachmann campaign manager Chase Kroll did not respond to requests for comment.

Like Bachmann, all Minnesota incumbents outspent their challengers, although Bachmann's race was the most lopsided.

Outside interests

In the closely watched Eighth District race, Republican Rep. Chip Cravaack raised about $2.3 million and spent nearly all of it. Democratic challenger Rick Nolan brought in about $1.2 million, making him the only winning Minnesota House candidate who actually raised less than the loser. Nolan won that race with 54 percent of the vote to Cravaack's 45 percent, unseating the Republican after he had served just one term in Congress. Both candidates were aided by massive spending from outside groups.

Cravaack amped up his spending in the final weeks of the campaign, pouring more than $1 million into the effort. Almost $800,000 of that went into a blizzard of ads as he struggled to counteract attack ads from Democratic groups.

On top of the money spent by Cravaack and Nolan, outside groups poured about $10 million into the northern district, much of that in hard-hitting ads. Theirs was the only Minnesota House race to attract significant spending by outside interest groups.

Bachmann, like other incumbent Minnesota congressional candidates, shared some of her largesse with her party. The day before Election Day, Bachmann transferred $40,000 to the financially struggling Minnesota Republican Party.

Democratic U.S. Rep. Collin Peterson, who raised just over $1 million for his most recent re-election campaign, was even more generous. He gave the Democratic Congressional Campaign Committee $250,000 -- including $100,000 the day after the election -- and donated $61,000 to the DFL Party.

The longtime western Minnesota congressman won last month's election with 60 percent of the vote, a 26 percentage-point advantage over Republican Lee Byberg. Byberg, who lost to Peterson by double digits two years ago, raised about $616,000 for his campaign, including $66,000 he lent to the effort. His campaign ended about $126,000 in debt.

Byberg joins Graves, southern Minnesota Republican Allen Quist and suburban Democrat Mike Obermueller in adding significant personal cash to their campaign quests. Graves spent $520,000 in his failed campaign to beat Bachmann; Quist spent $315,000 from his own bank account in his attempt to beat Democrat Tim Walz, and Obermueller lent his losing campaign against Republican U.S. Rep. John Kline $37,500.

Rachel E. Stassen-Berger • Twitter: @rachelsb