WASHINGTON — Ohio primary voters selected establishment candidates on Tuesday for the next big test of the Democrats’ promised “blue wave,” a House special election this August in the suburbs of Columbus that could indicate just how strong Democrats will be in November with college-educated, affluent voters.

After winning a six-way primary in central Ohio on Tuesday, Danny O’Connor, 31, a Franklin County official, will ask voters to send him to Congress on Aug. 7 to fill the House seat vacated by a long-serving Republican, Pat Tiberi.

The special election, which will take place 13 weeks before Election Day, will offer clues of Democratic strength, particularly on the kind of suburban terrain that will be critical in numerous races this fall as Democrats try to wrest control of the House.

Mr. Tiberi’s seat in the Columbus area has hardly been a swing district: It has been in Republican hands since 1983, when his predecessor, John R. Kasich, now Ohio’s governor, began his first term. But Democratic candidates in special elections for vacant House seats in more forbidding territory — including Arizona, southwestern Pennsylvania and South Carolina — have performed strongly since President Trump’s inauguration. And the makeup of the Ohio district suggests it could be fertile ground for a competitive — and expensive — race.