The battle for the Minnesota's Eighth Congressional District is being fought on Duluth debate stages, at chili fundraisers in Cambridge and lawn sign by lawn sign across the Iron Range -- but the heaviest artillery is being fired from far outside the state.

The sprawling Eighth is one of the nation's most hotly contested races, with millions of dollars pouring into the state from political action committees, super PACs and interest groups. Together they've dropped more than $4 million into the district so far, with nearly half a million dollars in just the past week.

That money is funding a blast of campaign ads that have hit Twin Cities and Duluth television airwaves like a toxic fog. Grainy black-and-white images fill TV screens as ominous music plays, warning that incumbent Republican Rep. Chip Cravaack is an out-of-touch Washington insider who wants to destroy Medicare, or that Democratic challenger and former Congressman Rick Nolan is an out-of-touch relic from the '70s who, incidentally, also wants to destroy Medicare.

"It's disquieting," Nolan said. "You spend a lifetime in a community, living, working, conducting your business, holding elective office, volunteer community service, and your friends and neighbors for the most part like you, respect you. And suddenly they're confronted with several million dollars of ads that are trying to tear down your good name, and some of your grandchildren come home from school crying about terrible things being said about Grandpa."

Shaking hands recently at a Cambridge veterans center chili fundraiser, Cravaack jokingly offered a disclaimer to a reporter: "Remember, if it doesn't say Chip Cravaack at the end of the commercial, I didn't have anything to do with it."

Swaying voters in a swing district such as the Eighth is crucial for Republicans and Democrats, with control of Congress potentially coming down to just 28 wild-card districts that could flip to either party.

Once a true Democratic blue, the Eighth has become one of those wild cards, starting with Cravaack's stunning upset in 2010. That's when the political neophyte unseated veteran Democrat Jim Oberstar, becoming the first Republican to represent the area in 63 years.

And the district has morphed again. Redistricting has pushed its boundaries so far that it now stretches in the north from International Falls to the tip of the Arrowhead, and in the south from Wadena to Chisago County.

With that, the district's political dynamic has shifted, too, bringing conservative southern exurbs in to clash with the traditional progressive politics of the Iron Range.

"We're seeing more outside spending in 2012 than we ever have before ... but it's not just about the money," University of Minnesota political scientist Kathryn Pearson said, noting that the jury's still out on whether negative ads really influence voters. "It's a seat where the Democratic Party has an advantage [but] it's going to be close."

The district is in the middle of an arms race, said Viveca Novak of the nonprofit Center for Responsive Politics, which monitors campaign spending. Both sides, she said, "are looking for the one ad that's going to punch through" and sway voters. And Minnesota hasn't seen anything yet. During the last three weeks of a campaign, she said, outside groups tend to double their spending.

Issues get lost

During a Tuesday debate in Duluth, Cravaack and Nolan went deep on issues that matter most to the district: the region's persistent unemployment, how to balance environmental protection without crippling the mining industry, whether bringing in new government infrastructure programs is worth adding to the federal deficit.

Not that you'd know it, though, if you got your election news from campaign ads. The more the outside groups fill the airwaves with attack ads, the harder it can be for the candidates to make their real message heard.

Cravaack spent two hours working the room, talking about the deficit, the Chinese military buildup. Ask what he's done for his district, and he points to his pro-labor votes and notes the times he's bucked his own party.

"When I take my card out and put it in the slot for my vote, I think of three things," Cravaack said. "I think, 'Is it good for the Eighth, is it good for Minnesota, is it good for the country?' And that's how I vote." Cravaack said he has "gone on record with some votes that are completely contrary to what my party wanted me to vote for, to the point that there was pretty heavy pressure that was placed on me."

A former airline pilot and union member, Cravaack says, "I'm what was called a lunch-pail Republican. I'm a pro-labor Republican."

Only challenger named

That might be an appealing message to get on the airwaves for a Republican running in a traditionally Democratic district. Instead, groups such as American Action Network, led by former U.S. Sen. Norm Coleman, will spend $626,630 on ads that don't highlight Cravaack's work on a single issue or even mention him by name. Instead, they just paint his challenger as "liberal" and "radical."

Likewise, when Nolan campaigns across the Eighth, he talks about new infrastructure projects that could get people back to work, the need to wrap up the "wars of choice" abroad, his belief that tax cuts for the rich do less to help the economy than programs aimed at helping the middle class.

He talks about his support for universal health care and his belief that environmental protections not only save the forests and lakes in the Eighth, but create tens of thousands of jobs along the way.

The interest-group ads from his side, however, train most of their fire on Cravaack, sniping at how much he spends to lease his official vehicle and how many town hall meetings he's held.

Of all the money spent on ads, more than 90 percent has been on opposition or attack ads. Less than 6 percent has been on ads supporting either candidate.

Nolan, who represented the old Sixth Congressional District between 1975 and 1981, said he is disturbed by the change that big money has brought since then, even when the money is spent on his behalf.

"I feel bad for Cravaack and his family and the others, as well. I've complained," Nolan said. "I can't have any direct control over these ads that are being run by outside groups against Chip Cravaack, any more than he has any control over the ones being spent and being run against me. But I have sent the message that I don't like them, I don't approve of them and I wish they wouldn't run them. If they're going to run something, you know, run something positive."

Jennifer Brooks • 651-925-5049