One of the nation's toughest congressional races seemed set last weekend when Minnesota Republicans endorsed former lieutenant governor Michelle Fischbach to challenge longtime U.S. Rep. Collin Peterson, one of a diminishing breed of rural House Democrats.

But a bitter convention fight spanning eight rounds of voting has called into question GOP unity in the rural western Minnesota Seventh Congressional District, which Peterson has represented in Congress since 1991. The voting was preceded by allegations of campaign finance violations and harassment, leading to a restraining order against a Fischbach press aide who has since left the campaign.

Peterson, an influential Agriculture Committee chairman, has faced increasingly aggressive GOP challenges in recent elections, holding on in 2016 even as President Donald Trump carried the district by 30 points. His challenger in the past two elections was Air Force veteran Dave Hughes, who could again be vying to take on Peterson in the state's Aug. 11 primary despite losing the party endorsement to Fisch­bach.

Hughes said in an e-mail message that he is not ready to say if he will run in the primary, citing "personal and professional responsibilities." Another GOP contender, Albany physician Noel Collis, said after the convention that he will still run in the primary, assuring a contested election.

Whether or not Hughes stays in the race, he remains a factor after pressing a complaint with the Federal Election Commission accusing the Fischbach campaign of violating campaign finance laws by allegedly coordinating with political action committees affiliated with groups that oppose abortion that are directed by her family members.

Fischbach's mother, Darla St. Martin, is co-executive director of National Right to Life. Fisch­bach's husband, Scott Fisch­bach, is the executive director of Minnesota Citizens Concerned for Life. Both groups endorsed her on consecutive days in January and made identical independent expenditures of $11,698.71 weeks later.

Fischbach's campaign described the FEC complaint as a "politically motivated stunt" and "gutter politics meant to divide the party" before the weekend's conventions. Fischbach campaign manager David FitzSimmons said this week that the campaign would seek to have the complaint dismissed.

Days before the weekend's conventions, Hughes also levied allegations against Fischbach's press secretary, Sam Winter, accusing him of bombarding him and his family with hundreds of phone calls during the endorsement fight. According to Hughes, Winter called him more than 300 times from April 4 to 27, including 60 times on a single day. Hughes described the calls as "coordinated attacks" timed to disrupt virtual campaign speeches.

Winter has since resigned from Fischbach's campaign amid misdemeanor harassment charges filed in Kittson County. FitzSimmons said he and Fischbach were unaware of the allegations before they surfaced ahead of the convention.

Despite the bad blood, Fisch­bach is seen by national Republican leaders as the party's best shot to defeat Peterson, a pro-gun, conservative Democrat and a well-known advocate for farmers over his years in the Legislature and Congress. Fischbach was recruited by the National Republican Congressional Committee, led by U.S. Rep. Tom Emmer, R-Minn., and has endorsements from Trump on down to state lawmakers across the district.

"We believe that this seat is going to be one of the seats that absolutely decides the majority, and so really the question people in this district are going to have to ask themselves is are they with President Trump or are they with Nancy Pelosi?" said FitzSimmons, a former chief of staff for Emmer.

Fischbach's entrance into the race quickly changed experts' assessments of Peterson's chances: Analysts from Larry Sabato's closely watched Crystal Ball at the University of Virginia and the Cook Political Report now grade the seat as a tossup.

Peterson announced in March that he would seek re-election, calling it a difficult decision "because our country is so polarized right now." But, he added, "that's also why I want to ask the voters of western Minnesota to support me again."

Democrats are seizing on the discord leading up to Fisch­bach's endorsement to try to puncture any sense of inevitability. DFL Party Chair Ken Martin accused Fischbach of being out of touch with western Minnesota farmers and instead "hoping blind allegiance to her political party will carry her lackluster campaign across the finish line."

While Hughes has not announced his intentions since Fischbach clinched the endorsement, his campaign's Facebook page lists a Sunday evening session via Zoom for delegates and voters.

Collis — who had more cash on hand than Fischbach at the end of the first fundraising quarter — and Hughes have both called Fischbach a "career politician," pointing to her decades in the Minnesota Legislature. Hughes has also staked out positions far to the right of Fischbach, such as calling for legalizing the possession of machine guns.

Republican leaders in the district are now trying to rally around Fischbach's campaign. Craig Bishop, who chairs the Seventh Congressional District's GOP Party, said it is "imperative for activists in CD 7 to look towards the future, not the past."

State Rep. Tim Miller, a Prinsburg Republican who has been in politics in the district since 2010, said "politics and identifying the right candidate … can be a little bit of a bumpy ride, but in the end I think the right person was endorsed."

Carlos Ramirez, chair of the Todd County Republican Party, expects voters to coalesce around Fischbach in November. But the recent history of voters there overwhelmingly backing both Trump and Peterson has him concerned.

"It's just the unknown vote: How do they vote for Collin Peterson in 2016?" Ramirez said. "It still stuns me how that happened."

Stephen Montemayor • 612-673-1755

Twitter: @smontemayor