As of this writing, that race is too close to call.
But as national correspondent Michelle Macaluso explains in the video above, both Republicans and Democrats say Tuesday's results are giving them momentum heading into November.
The battle in the Buckeye State is between Republican Troy Balderson and Democrat Danny O'Connor. The Ohio special election should've been a slam dunk for Republicans, who have controlled that seat for more than 30 years.
"What does the Ohio special election tell us about what to expect in the midterms?" Macaluso asked Georgetown University public policy professor Mark Rom.
"It tells us Republicans ought to be very, very nervous about the fall," he said. "The seats in Ohio should have been an easy win for Republicans."
Rom says Democrats are making things a lot closer than they should be.
Republicans poured millions of dollars into the 12th District -- an historically safe GOP seat and place that President Donald Trump won by 11 points.
"When the Democrats do 10-15 points better than you think they should, that suggests there's nationwide factors that are playing here, and that nationwide factor is Trump," Rom said.
But the president and Republicans are claiming victory in Ohio, pointing to Trump's help on the campaign trail in boosting Balderson's numbers.
Democrats paint a different picture, saying the president is getting their base to vote against him, pointing to the close numbers in the special election as a sign of what's to come.
About 60 Republican seats are seen as competitive. Democrats need to flip 23 seats to gain control of the House.
Both sides are convinced a wave is coming.