DUBLIN, Ohio (Reuters) - Becky von Zastrow often votes Republican in her affluent central Ohio suburb - but her dissatisfaction with U.S. President Donald Trump has convinced her to back the Democrat in a special-election test for both parties next month.

Democratic candidate Danny O'Connor meets with campaign volunteers ahead of a special election in Ohio's 12th congressional district in Dublin, Ohio, U.S., July 15, 2018. REUTER/Tim Reid

Her change of heart, reinforced by Trump’s handling of last week’s Helsinki summit with Russian President Vladimir Putin, could bode well for Democrat Danny O’Connor, a 31-year-old local officeholder running for an Ohio congressional seat Republicans have held since 1982.

In interviews with a dozen women, mostly Republicans, in the Midwestern state’s 12th Congressional District, several said they would buck their voting habits to support the Democratic candidate on Aug. 7, citing Trump as a major factor. Others said they disapproved of the president’s behavior but had yet to make up their minds about the congressional contest.

Strategists say winning over white, educated, suburban women in dozens of Republican-leaning districts will be key to Democrats’ efforts to retake the U.S. House of Representatives in Nov. 6 congressional elections. Democrats need a net gain of 23 seats to flip the 435-seat chamber and get a chance to block Trump’s legislative agenda.

Nationally, suburban women disapprove of Trump in slightly higher numbers than women who live in other parts of the country, according to Reuters/Ipsos polling. And those who disapprove of Trump are a little more enthusiastic about the November elections than those who like him.

That said, suburban women are just one faction within the Republican Party, and Trump’s approval numbers among all Republican voters have ticked higher over the past 12 months. In July, 84 percent of registered Republicans said they approved of Trump.

The Ohio race to fill a vacant House seat is the last scheduled special election in the country - and the last such snapshot of voter sentiment before the November elections, when all House seats and 35 of the 100 seats in the Senate will be at stake.

How well O’Connor fares against Trump-backed Republican Troy Balderson will signal whether Democrats can attract moderate voters unhappy with the president.

For von Zastrow and several other women in the Ohio district, Trump’s refusal at a July 16 news conference with Putin to criticize Russian interference in the 2016 U.S. presidential election affirmed their decisions.

“I was shocked. I don’t know why Trump said those things,” said von Zastrow, 51, who holds a master’s degree in business administration. The lifelong Republican voter declined to say how she voted in the 2016 presidential race.

Trump won the district - which stretches from wealthy Columbus suburbs into rural areas - by more than 11 percentage points in 2016.

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The race between O’Connor and Balderson appears close, analysts say. But Trump’s comments with Putin could be poorly timed for Balderson, said Kyle Kondik, a political analyst at the University of Virginia Center for Politics.

Balderson, a 56-year-old state senator, does not think Trump’s Helsinki remarks will hurt him.

“I disagreed with the comments,” he said in an email, adding that he did not consider Putin an ally of the United States. “I’m running to represent the people in Ohio’s 12th Congressional District and I trust that voters will see that.”

Balderson is a Christian conservative who supports Trump’s call for a wall along the U.S.-Mexico border. He also supports gun rights, opposes abortion and wants to repeal the Affordable Care Act, commonly known as Obamacare.

Trump endorsed him via Twitter on Sunday, writing that his fellow Republican was running “against a Nancy Pelosi Liberal who is WEAK on Crime & Borders.”

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Democrats are hoping for a repeat of Democrat Conor Lamb’s victory in March in a Pennsylvania district Trump had also easily clinched. A big swing in support from Republican to Democratic in the Pittsburgh suburbs, particularly among female voters, was a significant factor in Lamb’s win.

Like Lamb, O’Connor is running as a moderate and says House Democratic leader Nancy Pelosi should be replaced. The Franklin County recorder avoids attacking Trump as he knocks on doors in Dublin and New Albany, suburbs with large homes, well-tended lawns and good schools where household income and education levels far exceed national averages.

O’Connor tells voters he is engaged to a Republican and says he will work with Trump on infrastructure and the opioid crisis. He hammers messages about access to healthcare and moderate gun safety reform, which he says are the top issues for voters - particularly women - he meets.

Trump’s Helsinki comments appear to have given O’Connor another opening with this important group, though the candidate has refrained from tackling the remarks head-on.

“In Congress, I’ll put Ohio families first and be honest with anyone, including the president, who fails to represent our interests,” O’Connor said in a statement.

Since Helsinki, the president has said Russia did indeed meddle in the election. Still, several Ohio women who tend to vote Republican in congressional races but did not vote for Trump said the summit news conference was another disappointment.

“I am not sure if calling Trump a Russian asset is the right word, but I always suspected he was compromised in that regard,” said Tricia Kalmar, 43, who considers Pat Tiberi, the Republican congressman whose resignation triggered the special election, a family friend.

In a break from her typical Republican vote, Kalmar said she will back O’Connor over Balderson because of the Republican’s embrace of the president. She does not want a Republican “rubber stamp” for Trump representing her in Congress, she said.

Jill Siegel, 49, a mother of two in New Albany, where the median household income is over $191,000, said Balderson’s ties to Trump also were pushing her to vote Democratic next month.

“Trump’s comments in Helsinki did not sit with me well,” said Siegel, who said she voted for Democrat Hillary Clinton as a vote against Trump in 2016 but typically votes Republican in congressional races. “Why wouldn’t you trust your own intelligence agencies?”

But Balderson will get Nancy Smith’s vote. The 62-year-old Trump voter said O’Connor was too out of step with the district.

“I think he’s more liberal than he lets on,” she said.