Add the Ohio 12th District special election to the GOP's list of woes.

Fresh off a spectacularly underwhelming performance in Arizona’s 8th District special election, where Republicans spent more than $1 million to pull off a narrow victory, the party under Trump is facing more special election potholes in the immediate future.

In the latest sign of trouble for Republicans, the Cook Political Report officially swapped the status of the Ohio 12th District special election set for August from “lean Republican” to “toss up.” Republicans have controlled the district for more than three decades.

Many Democratic officials are viewing “toss up” races this year as being extremely vulnerable for the GOP, since there’s so much electoral momentum on the side of Democrats.

“All of the sudden, districts you didn’t think you could win in, you can win in,” Ohio Democratic Party chair David Pepper told CNN this week, while a GOP consultant in the Buckeye state conceded that race will be expensive, and competitive.

The special election is being called to fill the vacancy created by Rep. Patrick Tiberi, who resigned suddenly last winter. Tiberi is part of the large wave of GOP resignations and retirements ahead of the 2018 elections.

For Republicans, the math just isn’t on their side in the toxic Trump environment. That’s because in recent special elections, energized Democrats have routinely outperformed 2016 results, often by double digits.

In Tuesday’s special election in Arizona’s 8th District, a deeply conservative enclave, Republicans squeaked a five-point victory, when the same district voted for Trump by 21 points a year-and-a-half ago. Democrats hadn’t even bothered fielding a House candidate there since 2012.

And of course, in the March special election in Pennsylvania’s 18th District, Democrat Conor Lamb won in a region that had voted for Trump by 20 points. Lamb also badly outraised his Republican opponent.

As for Ohio’s 11th District, Trump won there by 11 points in 2016.

Special election concerns have even spread to places like Mississippi, which needs to fill a U.S. Senate vacancy this year. This spring, the conservative Weekly Standard warned, “Mississippi Is Now in Play for Democrats.”

Special elections aren’t always taken so seriously. The oddity this year is that Republicans are dropping like flies even with a Republican in the Oval Office. Sitting members of Congress are not only announcing their retirements at a historic rate, but some are flat-out quitting.

This week’s Arizona special election was required after Rep. Trent Franks resigned over a sexual harassment scandal. And on Friday, Rep. Pat Meehan (R-PA) became the latest Republican this year to announce his sudden departure from Congress — because he’s dodging an ethics probe.

As the Trump backlash spreads, Democrats could be landing wins in districts across the country they never even dreamed would be competitive.