Democratic Rep. Marcy Kaptur, the longest-serving woman in congressional history, will face a rematch with Republican Derek Merrin in a battleground northwest Ohio seat that grew a shade redder in redistricting. 

Merrin emerged as the victor in Tuesday’s five-way GOP primary in the 9th District. The former state representative had 43 percent of the vote when The Associated Press called the race just after 9:30 p.m. Eastern time. 

“Northwest Ohio is ready for fresh new leadership,’’ Merrin said in a statement. “After decades in Washington, [Kaptur is] part of the problem — not the solution.”

Merrin beat back several Republicans, including state Rep. Josh Williams, who had 26 percent of the vote, and former Immigration and Customs Enforcement deputy director Madison Sheahan, who trailed with 20 percent. Sheahan’s tenure as a top deputy under former Homeland Security chief Kristi Noem had come under criticism from her opponents.

President Donald Trump, who endorsed Merrin in the primary two years ago, stayed out of the contentious intraparty contest this time. 

Kaptur, who was unopposed in her primary Tuesday, is one of the House’s most vulnerable incumbents. First elected in 1982, she won her most recent contest against Merrin by less than a percentage point as Trump was carrying the district by 7 points.

But under the new lines approved by the state’s redistricting commission last fall, Trump would have carried the redrawn 9th District by 11 points, according to calculations by Inside Elections with Nathan L. Gonzales.

Still, Democrats expressed confidence that Kaptur would prevail in her bid for a 23rd term. 

“No one has been more dedicated to serving Northwest Ohio than Marcy Kaptur,’’ Washington Rep. Suzan DelBene, who leads the Democratic Congressional Campaign Committee, said in a statement. “Northwest Ohio rejected Merrin in 2024, and this November, they’ll do it again.”

Inside Elections rates the race Tilt Republican.

Key Senate race

Another significant contest was officially set Tuesday, with Democratic former Sen. Sherrod Brown taking on appointed Republican incumbent Jon Husted in the race to fill out the remainder of Vice President JD Vance’s term.

Brown breezed past first-time candidate Ron Kincaid in his primary, while Husted did not face a GOP opponent.

The race is an essential part of Democrats’ drive to win control of the Senate. Brown, a populist known for his rumpled suits and working-class values, is a formidable opponent and a prodigious fundraiser. Since his first election to the Senate in 2006, Brown had grown accustomed to winning reelection by fairly comfortable margins, even as Ohio moved further to the right.

But in 2024, with Trump on the ballot, Brown was unable to overcome his state’s GOP underpinnings. He lost to Republican businessman Bernie Moreno by nearly 4 points in one of the nation’s hardest-fought and most expensive Senate races. 

Meanwhile, the stage is set for another marquee statewide race in Ohio with 2024 presidential contender Vivek Ramaswamy securing the Republican nomination for the open governorship. He will next face Democrat Amy Acton, the state’s former public health director, who was unopposed in her primary. 

House races

In the 1st District, Democratic incumbent Greg Landsman and GOP challenger Eric Conroy will face off in the fall election for a Cincinnati-area seat that, like Kaptur’s district, became more Republican under the state’s new map.

Landsman defeated progressive Damon Lynch IV, who targeted the congressman over his pro-Israel stances. Conroy, an Air Force and CIA veteran who has Trump’s endorsement, easily prevailed in his primary. 

While the current version of the 1st District backed Kamala Harris by 6 points in 2024, Trump would have carried it under the new lines by 3 points, according to calculations by Inside Elections, which rates this fall’s race a Toss-up. 

The fields were also set for a trio of Republican-held House seats that Democrats are hopeful will trend their way in November.

In the Cleveland-area 7th District, union ironworker Brian Poindexter won the Democratic primary to take on second-term Republican Max Miller. Poindexter has the backing of Vermont Sen. Bernie Sanders.

In the 10th District, anchored in Dayton, Democratic hopes to unseat Republican Rep. Michael R. Turner rest with nurse practitioner and veteran Kristina Knickerbocker, who won a three-way primary Tuesday. 

And in the 15th District, outside Columbus, GOP incumbent Mike Carey will face Ohio State University professor Don Leonard, who edged out former state Rep. Adam Miller, the 2024 nominee.

Inside Elections rates all three races Solid Republican. 

Andrew Menezes contributed to this report.