A special election in a deep-red Tennessee congressional district could serve as a bellwether for next year's midterm elections, and CNN's data expert Harry Enten said the results will likely give Democrats a good feeling about their chances for retaking congressional majorities.

Democratic state Rep. Aftyn Behn and Republican Matt Van Epps will face off Tuesday for a chance to replace Republican Mark Green, who left Congress in July for a private sector job. Polling ahead of the election shows a much closer race than many expected.

"We can't make it to the end of the year without first holding a special election in Tennessee's seventh congressional district this Tuesday, and it is a ruby-red district in which the Democrats should not even come close to winning," Enten said. "It had a GOP rep — of course, that rep decided to step aside — and it's also a district in which Donald Trump has absolutely dominated. I mean, take a look at his margins in the past couple of elections: In 2016, he won it by 17 points. In 2020, Donald Trump won it by 15. In 2024, he won it by 22 points, a close GOP win on Tuesday. While it would still be a win, it would be a sign of weakness for the Republican Party."

"So what do we actually expect on Tuesday in Tennessee's seventh congressional district?" Enten continued. "We'll take a look here. ... The most likely outcome is a GOP win but by under 10 points, a 71 percent chance. Compare that to this, look at this: There's actually a chance of a Democrat win, a 15 percent chance of a Democratic win in a district that Donald Trump carried by 22 points, 22 points back in 2024."

"So even here, if the GOP wins by under 10 points, that most likely outcome is actually a very bad outcome for Republicans compared to the presidential baseline," he added. "We're talking about Democrats outperforming the 2024 presidential baseline by double digits."

Democrats have outperformed their 2024 results by an average of 15 points in special elections in Arizona, Florida, Texas and Virginia, and since 2005, parties that outperformed in special elections went on to win the U.S. House majority in the following election five out of five times, Enten said.

"It looks like the most likely outcome is Democrats outperforming the 2024 baseline by at least 10 percentage points, and that could be very, very good news for them come 2026," Enten said.

"Even if Democrats are not able to capture the seventh district, it is a very good sign for them going forward," he added. "Now, of course, we haven't held a special election yet. We'll have to wait and see what happens, and the midterm election is still, what, 11 months away? But at this point, all signs point to Democrats doing significantly better on Tuesday than they did back in 2024 in Tennessee's seventh congressional district, and when you put that together with the prior special House elections this year, it paints a very good picture for Democrats heading in to 2026."

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