The campaign to replace U.S. Rep. Tim Walz, shown in May, is heating up, with the GOP aiming to win back a Republican-leaning area held by a Democrat for more than a decade. (Tom Wallace — Star Tribune/The Minnesota Star Tribune)

WASHINGTON – National Republicans are hoping to flip the southern Minnesota congressional seat left open by U.S. Rep. Tim Walz's upcoming campaign for governor, aiming to win back a Republican-leaning area that DFLers have held for more than a decade.

Republicans have reason to feel emboldened. Walz's own winning margin last year was less than a percentage point, and President Donald Trump won the district by almost 15 points over Democrat Hillary Clinton.

"We are looking forward to this race," said Maddie Anderson, spokeswoman for the National Republican Congressional Committee, which announced plans to target the seat in February — before Walz announced his gubernatorial bid. Richard Carlbom, a DFL strategist who managed Walz's 2010 re-election campaign, acknowledged a tough fight.

"It's a very tough district," Carlbom said. "It's going to be a very hard district for Democrats to win."

The First District runs along southern Minnesota, extending from the Wisconsin border to South Dakota. It includes many small towns and rural areas along with the cities of Rochester, Mankato, Winona and Worthington.

Republican Jim Hagedorn, Walz's opponent last year, had already announced plans to run again. He noted the Walz campaign spent about $1.5 million last year, nearly four times what he spent. Hagedorn said he has talked to the GOP campaign committee since November and, "I do think they realized that if we had run a fully funded campaign that we would have won handily. "

Democrats are now faced with having to spend millions more than anticipated to hold the seat. Across the state, 2018 is shaping up as a competitive, expensive year of congressional matches: Republicans are again eyeing DFL U.S. Rep. Rick Nolan of northeastern Minnesota, and taking a new look at longtime DFL Rep. Collin Peterson in western Minnesota; both represent largely rural districts won by Trump.

At the same time, Democrats are also planning expensive races against Republican Reps. Erik Paulsen and Jason Lewis. Both represent largely suburban, Twin Cities-area districts, and both were public supporters of the failed Republican health care proposal.

"It's probably the most focused attention in congressional races in the state of Minnesota since I don't know when," said Brad Biers, a Republican strategist who has worked on several First District congressional campaigns.

Biers said even as a Republican, he views Walz as one of the DFL's best politicians.

"He's a heck of a firebrand when he wants to be, he's a heck of a stump politician. He's got to be one of the most talented campaigners they've got," Biers said.

Democratic Congressional Campaign Committee spokesman Tyler Law said Walz proved that a Democrat can win tough races in the district, "and that's exactly what we'll do again."

First District DFL Chairwoman Debra Hogenson said the party unit strongly supports Walz's run for governor, but with his departure "it's going to be more challenging. It always is when you don't have an incumbent."

She knows of several people exploring a run but said they're not ready to go public yet. Some DFLers have said that former state Rep. Terry Morrow of St. Peter, who has more recently worked for Walz, is a likely candidate.

Republicans cite as possible candidates state Sen. Jeremy Miller of Winona and Rep. Nels Pierson of Rochester, who used to work for Walz's predecessor, six-term GOP U.S. Rep. Gil Gutknecht. Another possibility is Olmsted County GOP Chairman Aaron Miller, who ran against Hagedorn in the 2014 primary.

Jeremy Miller said he had no intention of challenging Walz, but the announcement "is certainly a game-changer." He's received several calls from people asking him if he'd consider running for Congress, though he's not ready to make a decision and said he's focused on his work in the Legislature.

"I certainly didn't always agree with the votes that he took in Washington, but he was a very good communicator, he's a good politician and I had a good working relationship with him," Miller said of Walz. "I do believe it's a good opportunity for Republicans to take back that seat."

Minnesota GOP Chairman Keith Downey views 2018 as a great chance for Republicans to pick up seats in not only Walz's district, but also those held by Nolan and Peterson.

"It'll be a big year," Downey said. "We'll be a heavily targeted state with these races in play."

Maya Rao • 612-673-4210