Republican incumbent for Iowa’s 1st District, Rep. Mariannette Miller-Meeks, received a warning sign from a Monday poll, which placed her slightly behind her Democratic challenger.

The new generic ballot poll from the Des Moines Register shows a Republican trailing three points behind Democrat to fill the district's seat in the House. It is the closest race in the state, with Republicans favored in all three of Iowa's other House races.

Miller-Meeks defeated a Republican primary challenger earlier this year, and polls have shown alternating advantage for her and her challenger, Democrat Christina Bohannan.

The Register poll surveyed 811 Iowa adults, including 656 likely voters, from Sept. 8-11. The poll advertises a margin of error of 3.8%. The pollster did not name either candidate during the survey, instead asking respondents whether they favored having a Republican or Democrat fill the seat.

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Rep. Mariannette Miller-Meeks

Rep. Mariannette Miller-Meeks, Republican of Iowa, faces a 3-point deficit against her Democratic opponent, according to a new poll. (Mandel Ngan/AFP via Getty Images))

A spokesman for the Miller-Meeks campaign brushed off the poll in a statement to Fox News Digital.

"To extrapolate from 160 odd interviews when the pollsters didn't even ask a ballot where they named the candidates is next to worthless," the spokesman said. "But, yes, this is a competitive race, as Democrats and their backers have already spent millions of dollars on TV advertising distorting the congresswoman's record."

"Once voters understand how extreme Christina Bohannan is on the issues, we're confident that voters in the district will side with Mariannette Miller-Meeks," the statement continued.

The Des Moines Register/Mediacom Iowa Poll has found repeated swings in Miller-Meeks' district throughout the year. In June, the generic ballot poll ended in Miller-Meeks' favor, with a 53% to 41% matchup between a generic GOP candidate and a Democrat. The reverse was true in a generic poll in February, which had the Democrat leading 49% to 45%.

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Meanwhile, the Cook Political Report still has Miller-Meeks' district down as "Lean Republican." Fox News' power rankings also had the district as "Likely Republican" in August.

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Iowa's 1st Congressional district has flipped back and forth in polls throughout the year. (REUTERS/Eduardo Munoz)

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Some Republican voters in the Register poll expressed frustration with Miller-Meeks for not being supportive enough of former President Donald Trump.

"Our own Republicans are so milquetoast wishy-washy that they’re almost worthless, And that’s the category I would put Meeks in," Jim Schenk, a 62-year-old Republican told the paper.

"She’s just sitting there not doing anything," he added. "The only thing you can say about her is that she’s not actively harming us like a Democrat would be doing."

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Schenk said he believes Miller-Meeks has been hesitant to defend Trump because she knows she represents a vulnerable district.