In some ways, the race to determine Congressman Tim Walz’s Republican opponent seems backward.

State Sen. Dick Day of Owatonna has been active in southern Minnesota Republican politics for years, he’s a longtime elected official and, for nearly a decade, he was the guy charged with maintaining party unity in the state Senate. But Day is the insurgent candidate in the primary race, running a low-budget grass-roots campaign aimed at convincing voters to overrule the endorsement made by Republican activists.

Mayo Clinic oncologist Brian Davis wasn’t actively involved in Minnesota Republican politics until last year, and he’s never been elected to public office. But Davis is the GOP-endorsed candidate in the 1st District, has the party activists behind him, and has raised the money and organized the volunteers to run a traditional political campaign.

On Tuesday, voters in the primary election will decide which of the two will advance to the Nov. 4 ballot against Walz, a Mankato Democrat.

“I’m trying to do it the old-fashioned way, that’s one-by-one talking to people,” said Day, a 71-year-old former salesman who’s been in the Senate for 18 years and who was on the Owatonna City Council and the Steele County Board before that.

Day is hoping his long record of service, and the name recognition that comes with it, will help him Tuesday. He also notes he’s a Navy veteran who was “born raised and educated in the district.” And he’s hoping voters will think of him as an opinionated but straight-talking leader.

“Hopefully, they’ll recognize that I’m somebody who will stand up and say it like it is,” he said.

But Day wasn’t straight with Republicans about the endorsement, Davis said.

“He stated on numerous occasions that he would abide by the endorsement and not run in the primary,” Davis said.

Instead, Day announced in February he was skipping the endorsing convention and would challenge whoever was endorsed in the primary election.

“There are 430,000 voters in the 1st District,” Day said. “Why would you want 160 people to turn out on a Saturday and decide for you?”

Davis notes the 161 delegates elected to the convention sprung originally from the choices of nearly 7,000 Republicans attending precinct caucuses on Feb. 5. They studied the candidates and chose him.

“Winning the Republican endorsement is a reflection of the Republicans’ view on this race,” he said.

Davis, two decades younger than Day, has limited political experience, but his professional resume is long and unique. An Illinois native, he has a degree in nuclear engineering and worked on the licensing and design of nuclear power plants, according to his campaign biography. He earned master’s and doctoral degrees in mechanical engineering from the Massachusetts Institute of Technology and a medical degree from the University of Illinois.