Republicans have fared far worse in recent special congressional elections compared with previous elections. Republican margin of victory

A majority of the seats up for special election have historically leaned solidly to the right, and only two Republicans have lost in these races. Tuesday’s results remained too close to call, but Troy Balderson, the Republican candidate, had the biggest drop in support in all the special elections.

Mr. Balderson’s current margin is 36 percentage points lower than the 2016 margin of Pat Tiberi, the previous representative in that district. The average drop in margin for Republican candidates in special elections held from 2017 to 2018 was more than 20 percentage points.

Change in Republicans’ margins of victory Source: Offices of secretaries of state; Associated Press | Note: Data do not include races in which Republican candidates ran unopposed.

Since the district was drawn after the 2010 census, Ohio’s 12th has been solidly Republican. Mr. Trump carried it by 11 points in 2016 and Mr. Tiberi, won re-election by 37 points the same year. But Mr. Tiberi resigned earlier this year, fed up with Congress, and set in motion the race between Mr. Balderson, a Republican state senator, and Danny O’Connor, the 31-year-old Democrat.