WASHINGTON – U.S. Rep. John Kline's decision to retire from Congress has already touched off a fierce, bipartisan battle as eight candidates — and counting — are trying to stand out in what is emerging as one of the most costly and closely watched House races in the country.

So far, the race in Minnesota's Second Congressional District has drawn a health care executive, a former radio talk show host, an eye doctor, a former Red Wing mayor and a dairy farmer, among others.

Even though it is still about a year until voters head to the polls, the candidates have already poured more than $2 million of their own money into the race and are promising more.

"It's going to be extremely competitive," said Nathan Gonzales, editor of the nonpartisan Rothenberg & Gonzales Political Report, which studies House races nationally.

State Republican Party Chairman Keith Downey said he expects it to be difficult to hold a seat that Kline won for more than a decade — a perch he used to climb to star GOP status in Congress.

The district south of the Twin Cities is one of the most rapidly evolving political landscapes in the state, an area becoming more diverse and politically volatile. The district includes liberal arts colleges St. Olaf and Carleton and also the state's largest amusement park, Valleyfair.

Kline, who squeaked out his last Republican endorsement but then handily won re-election, has said that the 2010 reapportionment gave the district a far more Democratic lean than previous years.

"I think it's going to be a tough one," said Downey, who is banking on outside groups pouring money into the race.

These new dynamics are reflected in voting patterns. Residents reliably voted for Kline, a former U.S. Marine helicopter pilot with a strong record of supporting President George W. Bush, but they also came out big for Democratic Sens. Al Franken and Amy Klobuchar. Those same voters supported Gov. Mark Dayton's GOP opponent Jeff Johnson last year, but President Obama in 2012.

That ticket-splitting behavior makes the district an unusual battleground nationally.

Out of 435 elected members of the U.S. House of Representatives, only a dozen of those are considered "pure tossup" seats going into next year. Of all the 28 open seats nationally, the ones without an incumbent running, only eight are considered competitive.

Democrats see this as a rare chance to pick up a seat as they try to build momentum to one day win back control of the House. Republicans believe this is a perfect moment to bring in a fresh, likable and reliable candidate who, like Kline, could keep a tight hold on the seat and rise through the ranks on Capitol Hill.

"It makes it really appetizing for both parties. It's a swing district," state DFL Party Chairman Ken Martin said. "They [the candidates] are going to have free rein in buying in this media market. There won't be other campaigns. Even the presidential … will be a sort of back story."

Adding to the suspense is that both sides have candidates who have not agreed to play by party rules and abide by the political endorsement process.

Among the three Democrats who have filed paperwork to run, former health care executive Angie Craig, ophthalmologist Mary Lawrence and dairy executive Roger Kittelson, Lawrence said she is undecided on whether she will drop out of the contest if she is not endorsed by party delegates at the DFL convention in May.

Candidates are hunkered down calling delegates and trying to raise money. In a stunning and early display of her commitment, Lawrence has given more than $1 million of her own cash to her campaign. In his last re-election, Kline raised $2.7 million to win, for instance.

"I expect to win," said Lawrence, noting she put her own money in so voters understood she had "skin in the game."

"I want people to know that I care deeply about this and I'm going to ask people to volunteer their time and money, they should know that I'm also doing the same."

Among the Republicans running so far are engineer David Gerson, former Red Wing Mayor and state Sen. John Howe, former radio host Jason Lewis, former state Rep. Pam Myhra and David Benson-Staebler, an online commerce executive and former DFL operative running on the GOP side.

Howe has said he wasn't sure he would abide by the endorsement, either. Howe also pledged to give a few hundred thousand dollars to his campaign. Gerson has also given himself money.

Former radio show host Jason Lewis has said he will abide the endorsement process only "if it's a fair process."

Lewis hedged: "Unless someone tries to pull a fast one."

The early intensity of the race is increasing the stakes. Candidates must be careful to ensure their campaigns have the enthusiasm and the money to slug it out all the way to the August primary — and win it. Then they will need to quickly marshal their volunteers, connections and money for the general election.

At the moment, the candidates are focused on winning over those in their own party.

So far, the Democrats have been fundraising, working on endorsements, attending parades and going to various smaller events trying to meet other Democrats.

"The state of the race out here for me is very focused on the DFL endorsement," Craig said. "Working on name recognition here over the summer is going to pay dividends when we get to the general election."

Among the Republicans, the sprawling field means that the candidates are toiling to stand out — especially Lewis and Howe. At a recent Republican forum in Inver Grove Heights, the two hammered each other over Minnesota Vikings stadium subsidies and domestic policy as they fought to prove their conservative credentials.

Yet, some are mindful of the delicate course they must chart, appealing to conservative activists so crucial at this stage while not alienating independent-minded voters from the other party.

"The Republicans need to nominate the most conservative yet electable candidate and that's who I am," Howe said. "I'm not repulsive."

Some voters in the district, reflecting a less divisive political temperament, are not looking for firebrands eager to dig in over party ideology.

Burnsville Mayor Elizabeth Kautz said the lurching federal budget deals — including transportation — have been especially frustrating as a city leader seeking federal dollars for local project help.

"They just need to start talking and making good decisions," Kautz said. "We have to be talking to everybody and bringing people together and gaining consensus. We know we have to make good decisions if we want our cities to be vibrant."

Staff writer Ricardo Lopez contributed to this report.

Allison Sherry • 202-383-6120