President Trump’s recent spate of tariffs are popular among his working-class supporters here. But his aggressive trade moves could help put a key Senate seat out of reach for his fellow Republicans, undermining the GOP’s fight to keep control of Congress in November.

Democratic Sen. Sherrod Brown is running for reelection partly by touting his support for the president’s aggressive trade strategy and trumpeting his longtime opposition to the North American Free Trade Agreement and other trade deals Trump rails against. That’s largely a boon in Ohio, where Trump won by 8 percentage points in 2016.

“I’m working with the president to make these tariffs work,” Brown said last week after addressing a gathering of Teamsters at a United Steelworkers hall in Akron.

For Brown’s likely Republican opponent, Rep. James B. Renacci, Trump’s trade moves are a growing political headache, forcing the candidate to explain his own past support for trade pacts and his concerns about the tariffs.

It’s a challenge that was compounded Wednesday when China threatened to retaliate with tariffs on U.S. soybeans, cars and airplanes — critical cogs in the Ohio economy. The threats sparked widespread anxiety among farmers and potentially created even greater complications for Renacci, who is trying to broadcast his support for Trump while also navigating around a policy that could hurt voters who usually vote Republican.

“I want to just continue to work with as many constituents in Ohio and make sure that we don’t have any window between what the president wants to get done and what Ohio businesses and the economy really need,” Renacci said in an interview in Columbus.

Other Republicans are likely to face Renacci’s challenges as they defend their party’s two-seat Senate majority and try to keep Democrats from picking up the 23 seats they would need to retake the House. Brown is one of 10 Senate Democrats running for reelection in states Trump won, and analysts say the two-term lawmaker is in a strong position, in part because his populist approach on trade now aligns with Trump’s rhetoric.

Renacci, like GOP lawmakers elsewhere, is being forced to explain to blue-collar voters why he supports free trade policies that are now out of step with Trump’s Republican Party.

“In the context of politics there may be some people, including Trump people, who say ‘Whose side are you on?’ ” said Herb Asher, a professor emeritus of political science at Ohio State University. “And it’s easier for Sherrod to answer that question than Renacci.”

Similar upside-down trade politics could emerge in House races, too, in districts from California to Washington state to Michigan. In the 7th District in southern Michigan, Democratic challenger Gretchen Driskell has embraced Trump’s trade moves, praising his steel and aluminum tariffs while criticizing her opponent, Republican incumbent Tim Walberg, who has a history of supporting trade deals.

In Indiana, Democratic Sen. Joe Donnelly has also spoken in favor of Trump’s tariffs, and he, like Brown, could end up facing a Republican House member with a history of embracing free trade deals.

Ohio, like other states in the Midwest, remains reliant on manufacturing industries despite having bled tens of thousands of jobs in steel and other industries over the years. Mills shuttered by the dozens during the 1970s and 1980s, putting well-paid steel and iron workers into unemployment and devastating once-prosperous communities like Johnstown and Warren.

While a variety of factors contributed to the manufacturing decline, many workers blame unfair foreign competition, including countries like China and South Korea “dumping” steel at below-market prices that domestic producers could not compete with. Now, many see hope in Trump’s announcement of 25 percent tariffs on imported steel and 10 percent on imported aluminum.

Although few argue that Ohio’s steel production industry can be restored to its glory days, steelworkers here hold out optimism that some idled facilities could be restarted and some jobs brought back. Following the tariff announcement, Republic Steel announced plans to restart an idled furnace in Lorain, Ohio, with the potential to bring back 1,000 jobs. In Granite City, Ill., U.S. Steel said it would restart one of two blast furnaces and bring back 500 workers.

“We’re hoping the steel tariffs could just put the industry back on a level playing field,” said Patrick Gallagher, a subdistrict director for United Steelworkers in Cleveland.

Union leaders in Ohio and elsewhere watched in frustration during the 2016 election as significant portions of their workforce ignored union endorsements of Democrat Hillary Clinton and voted for Trump instead. Jack Hefner, president of United Steelworkers Local 2 in Akron, estimated around a third of his membership voted for Trump despite the leadership’s support for Clinton.

“Labor’s been beating the drum that these trade deals are bad, so here comes Trump saying the same thing, which made it really hard for us,” Hefner said. “He stole our playbook.”

Brown’s alliance with Trump on the issue can only help him with such voters, Hefner said. He said he had spoken with several union members who cast their ballots for Trump in 2016 but intended to support Brown’s reelection.

“I don’t imagine he and Donald Trump are going to go out and have a beer anytime soon, but on trade and jobs, Donald Trump talks the talk. We’ll see if he walks the walk,” Hefner said. “If he does what he says he’s going to do on these trade issues, he’ll have an ally in Senator Brown.”

Until Trump came along, free trade was a core GOP tenet and remains so for many GOP donors and Chamber of Commerce Republicans who typically help Republicans win elections. But given the steel industry’s strong history in the state, along with the emotional appeal of Trump’s “Buy America” refrains, support for his tariffs appears to stretch well beyond union halls, despite the potential economic downsides. When Trump visited the state last week to deliver a speech about infrastructure in Richfield, the crowd waiting for him included two women in pink hard hats holding signs that said “Thank You for Supporting American Steel” and “Our Steel Industry Thanks U.”

One of these women, Sherry Slocum, said she works at a local company called Belden-Hutter that helps manufacturers sell power-transmission products.

“I foresee good things” from the tariffs, said Slocum, a Republican who said she voted for Trump. But Slocum wasn’t ready to say who she would support in the Senate race, saying, “That one’s going to have to play itself out.”

Such voters may present an opportunity for Brown to peel away some Trump supporters based on their views on trade and his ability to present himself as the president’s ally on an issue so ingrained in the culture of the state. Brown has a long-established record on the issue and even wrote a book more than a decade ago called “Myths of Free Trade.”

He has partnered with Republicans on the issue, including work with Rob Portman, the state’s Republican senator, on legislation called the Leveling the Playing Field Act, which aimed to give businesses more recourse to challenge unfair foreign competition.

In an interview, Portman cited his joint work with Brown on the issue and said he wasn’t sure where Renacci stood.

“I don’t know what Renacci’s position’s going to be. I just don’t know. But as you know, Brown and I work together on this stuff,” Portman said, going on to advocate a “nuanced position” on tariffs.

“We need to have a level playing field and fair trade but that doesn’t mean that you want to slap on protectionist tariffs without, you know, a fair-trade reasoning behind it. It invites retaliation and causes big downstream costs to our consumers,” Portman said. “So I think there’s a balance here.”

Brown refused to speculate on the political ramifications of his views or the fact that a Republican president now holds positions he has long advocated.

“Believe it or not, I don’t care. . . . I don’t mind supporting or opposing presidents in either party on trade,” Brown said in an interview at the steelworkers hall in Akron.

On Trump’s tariffs, Brown said, “I can quarrel with how he did it, how he rolled it out, I can quarrel with he punished Canada initially more than China . . . but fundamentally it was the right thing to do” and will “be a net positive for the national economy.”

Renacci, a four-term House member and former accountant who founded a company that owned and operated nursing homes, has his own track record on trade, but his includes voting for the deals with Colombia and the one with Korea that Trump is now renegotiating.

“I’m someone who is a big supporter of the president and his agenda and the direction he’s taking. I do think we have some unfair trading partners with China, so I’m glad to see we’re doing some of the things we’re doing with China,” Renacci said. “I’m close, but in the end, I want to also talk with the constituents who are going to be most affected.”

Correction: A previous version of this story incorrectly described the products China has targeted for tariffs. The products include U.S. airplanes, not airplane parts.