A special election Tuesday in a traditionally Republican district in Ohio will be the last tune-up before the November midterm elections that will determine control of Congress.

As if Republicans needed another warning ahead of what could be a tough election, polls show a basically 50-50 race in a district President Donald Trump won by 11 percentage points in 2016.

“It looks like it’s going to be a close race,” said Christopher Devine, a political science professor at the University of Dayton. “Based on past history, it shouldn’t be.”

In addition to backing Trump and 2012 GOP nominee Mitt Romney by double digits, the 12th District has sent Republicans to Congress for decades. Pat Tiberi, whose resignation triggered the special election, easily won nine elections.

Before that, John Kasich — who now is the state’s governor — held the seat dating to his defeat of Democratic incumbent Bob Shamansky in 1982. Kasich was chairman of the House Budget Committee following the GOP Contract with America congressional takeover in 1994.

Other than Shamansky’s aberrational victory in 1980, the last time the district elected a Democrat was in 1938.

But the last two polls have been within the margin of error. A Monmouth survey last month suggested Republican state Sen. Troy Balderson (pictured above right) had a 1-point lead. A poll by Emerson College released Monday gave Democrat Danny O’Connor (pictured above left) a 1-point lead.

The district, which curves around Columbus, has loads of suburban voters who have been lukewarm toward Trump. Democrats have had success during the Trump presidency in pulling off upsets or near-upsets in these types of districts.

Spencer Kimball, an adviser to the Emerson College Polling Society, said polling and voting results in special elections have shown an unusually high level of engagement by Democratic voters.

“You’re seeing a lot of energy from people who voted for [2016 Democratic presidential candidate] Hillary Clinton,” he said, “similar to what Trump was getting in the 2016 election.”

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Kimball said Republican support for Trump remains strong, although not quite as potent.

“He’s still getting 90 percent of the Republican vote,” he said. “But he’s not getting 95 percent of the vote. So there’s a bit of a melt there.”

The other big difference, Kimball said, is that independents are breaking more toward the Democrats.

Republican National Committee Chairwoman Ronna McDaniel on Tuesday downplayed the significance of the voting Tuesday.

“Every special changes the dynamic. And we’ve been saying this from the very beginning of these special election. Turnout’s an issue. You can’t predict who’s gonna come to the polls in August on a nontraditional election day,” she said on “The Laura Ingraham Show.”

The May primary did not suggest a blue wave in August. Some 67,133 voters cast ballots in the Republican primary, compared with 43,885 who voted Democrat. But early voting appears to be favoring Democrats. Voters who participated in the Democratic primary have outvoted those who voted in the GOP race by 23 percentage points in early balloting.

What’s more, O’Connor has outraised and outspent Balderson, according to campaign finance reports.

Trump swooped into Ohio on Saturday in an attempt to save the seat for the Republicans. His support cuts both ways in a general election, but McDaniel said it was helpful for Balderson.

“There’s nothing that can better fire up the Republican base right now than President Trump.”

“We needed him to go in and get our voters engaged,” she said. “A lot of them were not paying attention.”

Devine said special elections tend to have lower turnout, which makes each party’s base more important.

“There’s nothing that can better fire up the Republican base right now than President Trump,” he said.

The Ohio race is not the only contest on the ballot across the country Tuesday. Republicans and Democrats are holding primaries in Kansas, Michigan, Missouri, and Washington state.

The most closely watched of all those races likely is the Kansas gubernatorial race, where Secretary of State Kris Kobach is taking on incumbent Jeff Coyler, who became governor when Sam Brownback left office to become Trump’s ambassador at large for international religious freedom.

Polls suggest the race is close. A Trafalgar Group survey released Sunday had Kobach up by 7 points, while a Remington Research poll released Monday gave Coyler a 2-point edge.

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Trump waded into the race on Monday, endorsing Kobach, who served as vice chairman of the president’s voter fraud commission. Kansas University political science professor Burdett Loomis said the late endorsement may help Kobach at the margins, but he added that most Trump partisans probably were with the secretary of state anyway.

“I don’t think before Trump’s endorsement that anyone didn’t realize that he was the Trump candidate,” he said. “It could have the opposite effect. Kansas has a lot of moderate Republicans.”

Loomis said he believes conventional wisdom is right that the Democrats have a better chance of winning back the governor’s seat if Kobach is the GOP nominee.

“This is a huge election for Kris Kobach, and it either moves him into the governor’s election, or it — I wouldn’t say it ends his career, but it puts a crimp in it,” he said.

Devine, the University of Dayton professor, said a smaller-turnout election tends to favor the party with the more fired-up base.

“The electorate that’s going to be casting those votes in November is just different,” he said. “How different, I don’t know.”