With most of the votes counted, the two candidates traded a lead of just a few hundred votes. That narrow edge came in a district anchored in suburban Columbus, Ohio that President Trump won by 11 percentage points in 2016 and hasn't elected a Democrat in 35 years. There's an automatic recount if the margin of difference is within 0.5 percent, and the Columbus Dispatchnoted that provisional ballots and absentees sent from overseas and the military won't be counted for 10 days.
Trump also endorsed Kansas gubernatorial candidate Kris Kobach, and Tuesday's GOP gubernatorial primary results in the Sunflower State will be another test of how much GOP primary voters value Trump's endorsement.
People leave a polling station during Tuesday's special election in for the Ohio's 12th congressional district in Newark, Ohio, U.S., August 7, 2018.
But Trevor Moffitt, a public health doctoral student at The Ohio State University who voted for O'Connor, said he felt Balderson's attacks on Democrats went too far.
If you intend to vote in today's primary, you will need to either already be registered as a Republican or Democrat or declare a party affiliation at the polling place.
The 12th district has numerous hallmarks of areas that could be weak spots for Republicans this cycle - well-educated, relatively affluent suburbs that may have soured on Trump and are looking to register their frustration through their midterm vote. So far the answer has been no. It's a bellwether, one the Democrats see as a sign of a blue wave if they win or come very close.
Republican outside groups spent more than $5 million combined to salvage Balderson's prospects in the race after he was vastly out-raised by O'Connor. After my speech on Saturday night there was a big turn for the better. "Any Republican running for Congress getting vastly outraised by an opponent needs to start raising more money". So, as Republicans like Ohio Gov. John Kasich - a vocal critic of Trump - pointed out prior to Election Day, the sheer fact that the race is so close should strike fear in the hearts of GOP operatives.
But it isn't entirely clear if Trump's support will ultimately help or hurt Balderson on Tuesday.
Cory Bliss, executive director of the Congressional Leadership Fund, a Republican-aligned SuperPAC, said: "While we won tonight, this remains a very tough political environment and moving forward, we can not expect to win tough races when our candidate is being outraised". Troy Balderson in a district that has been in GOP hands since before the 31-year-old Democrat was born.
Republicans were hoping for Democratic discord in Kansas' 3rd Congressional District, a suburban Kansas City district where several candidates were fighting for the chance to take on Republican Rep. Kevin Yoder in November.