After Alexandria Ocasio-Cortez's stunning victory in NY against Rep. Joe Crowley, progressives hope to demonstrate that their policies can win over voters in the middle of the country.
Other Republicans had also rushed to Balderson's aid.
Voters on Tuesday are choosing would-be successors to Republican Gov. Rick Snyder, who can not run again due to term limits, and a GOP nominee to face third-term Democratic Sen.
Democrats looking for a shocking underdog win in a special election in OH on Tuesday are hoping not only to snatch a House seat in a historically Republican district, but also to energize their national effort to fight President Trump's agenda and reclaim a congressional majority.
A win by O'Connor would show that some of the GOP's most familiar attack lines may not prove salient any longer come November. At one point in the campaign, Balderson couldn't name a single area of disagreement but since cited differences on tariffs and immigration.
The central OH race was the marquee contest on a day when four other states held nominating contests, including a battle for governor in MI in which a mainstream candidate beat a progressive, and a high-profile conservative challenge to the incumbent Republican governor in Kansas.
"I'm just exhausted of the rhetoric of 'They're the bad guys, we're the good guys, '" said Moffitt, 29, of Westerville. Described by campaign operatives as a "Whole Foods" district, the largely suburban region features a more affluent and educated voter base than the typical Trump stronghold.
At times, the race centred on Trump's tax cuts as much as the candidates.
5 dead after plane crashes into California mall parking lot
Ella Pham and her boyfriend were walking across the lot Sunday when they saw the twin-engine Cessna plummet. Dashboard from a vehicle in the area shows the plane as it nose-dived to the ground.
President Donald Trump is greeted by 12th Congressional District Republican candidate Troy Balderson as he arrives on Air Force One at John Glenn Columbus International Airport in Columbus, Ohio, Saturday, Aug. 4, 2018.
O'Connor and his Democratic allies railed against the tax plan, casting it as a giveaway for the rich that exacerbates federal deficits and threatens Medicare and Social Security.
Mr Balderson and his Republican allies have backed away from the tax plan in recent weeks, training their fire instead on top House Democrat Nancy Pelosi.
O'Connor dominated Balderson on the local airwaves.
Voters in suburban Detroit will also weigh in on the direction of the Democratic Party.
And in suburban Seattle, three Democrats are vying in a jungle primary for the seat held by another retiring Republican, Rep. Dave Reichert.
The field was set in two Senate contests as well.
Mr. Hawley, the Missouri attorney general, advances to face Democratic Sen. Pat Tiberi resigned earlier this year, has taken on outsized importance for clues as to how big of a blue wave could be forming to help Democrats take back the House come November.
Iraq War veteran John James also won the Michigan GOP Senate primary to take on Democratic Sen.