Missouri voters have spoken, and the race for governor this November will be between a Republican who used to be a Democrat and a Democrat who used to be a Republican.

Former Navy SEAL Eric Greitens emerged from a spirited primary to win the Republican nomination Tuesday night, besting businessman John Brunner, former Missouri House Speaker Catherine Hanaway and Lt. Gov. Peter Kinder.

He’ll face Missouri Attorney General Chris Koster, who easily won the Democratic nomination.

The contest creates a strange dynamic: Until recently, both men were members of the other political party.

Greitens, 42, returned to Missouri after his time in the military to start The Mission Continues, a nonprofit that connects veterans with volunteer opportunities in their home communities.

He has never sought elected office before, but did flirt with a run for Congress as a Democrat in 2010. Additionally, he attended the Democratic National Convention in 2008. He says he was raised a Democrat by his parents, but after serving in the military and starting his nonprofit, he was “made a conservative, not by birth but by conviction.”

His campaign focused on what he said was a need for a political outsider to lead state government.

“We have a culture of political corruption in Jefferson City,” Greitens said. “We have corrupt politicians, well-paid lobbyists and special-interest insiders taking the state in the wrong direction.”

Koster served 10 years as Cass County prosecutor before being elected to the Missouri Senate as a Republican in 2004. He was eventually chosen by his Republican colleagues to be their caucus chairman.

His career in Republican politics came to an end in 2007, when Koster publicly split with the party and declared that “Republican moderates are all but extinct.”

A year after he switched parties, he was elected attorney general as a Democrat. He cruised to re-election four years later.

While he differs with the base of his party on a number of high-profile issues — most notably his opposition to gun control legislation — he has quickly become the heir apparent to outgoing Democratic Gov. Jay Nixon, who is being forced from office because of term limits.

In a speech to supporters Tuesday night, Koster said he became a Democrat because “I saw the Republican Party heading down a dark alley with no escape.”

“Tomorrow morning, you will see the ads against me begin, telling you what a horrible person I am,” he said. “The ads will be paid for by the very same conservative politicians who once chose me as their leader.”

Koster faced only token opposition in the gubernatorial primary, winning nearly 80 percent of the vote Tuesday against three opponents who barely mounted a campaign. He has more than $10 million in his campaign war chest, thanks in part to more than $4 million in contributions from organized labor unions.

But while Koster has a big fundraising advantage as the general election kicks off, Greitens has proved he can raise money in a hurry.

Greitens has nabbed checks from out-of-state donors like Las Vegas casino mogul Sheldon Adelson, who donated $200,000 to his campaign last month. Most recently, he got a $1.9 million check from a Washington, D.C.-based political action committee called SEALS for Truth. The donation is the largest single contribution to a candidate in Missouri history.

The massive infusion of dark money into the primary riled his opponents, who accused Greitens of hypocrisy for preaching an anti-corruption message while awash in out-of-state anonymous money. But it wasn’t the first time one of his donors caused a stir.

Silicon Valley investor Michael Goguen, who donated $1 million to Greitens, was sued by a woman who claims he sexually abused her for more than a decade, agreed to pay her $40 million in response and then only gave her $10 million.

Goguen has vehemently denied the allegation and is countersuing the woman alleging extortion. But Greitens faced repeated calls by his fellow Republicans to return the money, which he has refused to do.

When one of Greitens’ rivals said during a TV debate that Greitens had accepted money from “a guy who took $1 million from the owner of a teenage sex slave,” Goguen sued, claiming he had been defamed.

Democrats joined in the criticism when the Goguen donation was mentioned in a last-minute attack ad funded by a national Democratic political action committee with ties to Koster.