As Democrats in the 8^th District head to the polls this week, there’s a feeling that any of the three DFLers on the ballot could walk away a winner.

Democrats will choose a candidate Tuesday to take on freshman Republican U.S. Rep. Chip Cravaack in November. It’s the first competitive DFL primary in the district since the 1970s, and with the lack of recent precedent (or public polling), supporters, advocates and political experts don’t know whether Tarryl Clark, Rick Nolan or Jeff Anderson has a district advantage going to the polls.

To be sure, all can stake some claim to some semblance of an edge: Clark is a top fundraiser and her campaign has outspent the other two; Anderson has the deepest roots in the district and has been leveraging that against two opponents he paints as outsiders; and perhaps most influential of all, Nolan has the DFL’s backing and is campaigning with its full force at his back. But it’s tough to say whose edge is greatest, especially given the way the district and its demographics have changed since the last time its DFLers were asked to settle an intra-party power struggle.

“The changes in the last decade or two have made it almost a different district,” University of Minnesota history professor Hy Berman said. “Whatever has happened historically, I wonder if it has any bearing on the present day.”

Here are some storylines to watch  Tuesday:

How will the Iron Range vote?

The Iron Range is one of the most traditionally Democratic strongholds in Minnesota, and it will account for a large share of the voters who turn out, making it a key focus for any DFLer running in the 8th.

“You go mining where the mineral is,” former U.S. Rep. Jim Oberstar, a Nolan supporter who represented the district for 36 years, said. “The mineral is on the Mesabi Range, Carlton County, Lake County, Cook County, Koochiching County, St. Louis County and Itasca County.”

Anderson, true to his “buy local, vote local” campaign theme, has said he’s focusing on increasing his turnout in the district’s Iron Range, which will make up the core of DFL primary vote.

It’s a strategy Berman said should paid off, historically, but, as the Star Tribune noted this weekend, the Iron Range and the counties it makes up are shrinking. And given Oberstar’s three-decade hold on the district, this will be the first time a smaller Range will try to flex its political muscles in a district-wide DFL contest.

That makes it hard to predict how Iron Rangers will vote, though Berman said Anderson’s “one of us” message might not make as serious an impact on the Range as it once might have.

“The old sensitivities that used to exist about outsiders … I don’t think that’s as strong a feeling any more,” Berman said. “The insularity of the Iron Range has diminished to an extent.”

As for the Clark and Nolan campaigns, both say they’re running district-wide races, with caveats: Nolan as the weight of the DFL behind him and he’s using its resources to drive get-out-the-vote efforts around the district. Clark, meanwhile, is using paid media in the Duluth media market and relying on old-fashioned retail politicking in the L-shaped mass of counties that make up the western and southern edges of the district.

And no matter how the primary turns out, the traditionally Democratic lean of the 8^th, and its backbone on the Iron Range, will be tested come November.

“It’s still fundamentally a DFL district,” Berman said,  “but not to the extent and degree that it was before.”

What effect will ads have on the race?

All three candidates and their backers are airing television or radio ads ahead of the primary, and though Anderson and Nolan have biographical spots on the air, it’s an attack from Clark that has garnered the most buzz.

Clark began airing the spot in Duluth on Wednesday, hitting Nolan for his time running the Minnesota World Trade Center organization 20 years ago. It’s her closing argument: Nolan was ineffective as a potential job creator at the WTC, so, as former President Bill Clinton implored voters (by way of a video from a 2010 campaign rally), “you need Tarryl Clark in Congress.”

Immediately Thursday, the DFL Party began airing a blistering radio spot accusing Clark of hypocritically attacking her opponent. Nolan, meanwhile, called the ad “gutter politics” and worked to rebut its key points in a press conference and at campaign events late last week (for his part Anderson declined to take sides when he was asked about the issue at a KSTP debate over the weekend).

Given her fundraising edge, Clark has been running television ads since June and has been able to have a larger presence than Nolan or Anderson on the 8^th’s airwaves. Outside groups have focused on the race as well. The DFL has spent more than $155,000 in TV ad and radio ads this month, and Emily’s List spent $85,000 to produce and air ads on Clark’s behalf. No outside groups have spent to back Anderson’s campaign.

How do the candidate’s messages play?

As with any primary election, these three candidates have essentially tried to convince voters of two things: that they’re strongest, bluest DFLer in the contest and that they are best able to beat the incumbent Cravaack.

That means appealing the district’s Democratic-leaning constituencies. Oberstar, a former chairman of the House Transportation Committee, said voters in the construction trades will look for someone who supports increasing federal investment in infrastructure (all three candidates have said they want to be on the transportation committee). Nearly everyone agrees that the 8^th’s “natural resources-based” economy should be a priority and candidates should support policies that enable new mining and more shipping from the port in Duluth.

“Without mining, there is no northeastern Minnesota, it’s as simple as that,” said retiring state Rep. Tom Rukavina, an Anderson supporter from the Iron Range. “As the Range goes, so does Duluth. I think this election is going to be about that.”

In general, the candidates themselves differ only slightly on the issues they would confront in Washington (Nolan, for example, sits a bit to the left than his opponents on foreign policy and health care, and though they all support expanded mining, there are slight differences to their positions). That means much of their arguments are based on why they’d be best to take on Cravaack in November.

Dan Hartman, the president of the Duluth City Council and an Anderson supporter, said that should be the first thought on DFL voters’ minds next week (he used his candidate’s line, as well: “In order to win this November, you’ve got to win the Range”). To that end, the candidates have different messages for the voters (as they told KSTP this weekend):

• Anderson emphasizes his roots in the district: “Living in northern Minnesota matters,” he said. “I think people in the 8^th are looking for new, homegrown 21^st century leadership that can go to Washington and represent their values and what’s important to them.”

• Clark’s focus is firmly on Cravaack, and she goes after him for supporting Republican budget resolutions that look to reform the way Medicare is funded: “I want to go to make sure we’re actually doing things that are right for our families and communities, getting us back to be primaries in Washington.”

• Nolan said his goal is to mobilize Democrats who either voted against Oberstar in 2010 or skipped voting altogether. “Democrats need to take a look and say, who can win this? I’ve won congressional elections. … I’ve got a pretty good feel for what people want and expect and I could win this election for the Democrats and help get this country back on track again.”

Devin Henry can be reached at dhenry@minnpost.com. Follow him on Twitter: @dhenry