Ohio special election Tuesday watched for clues to Nov.

Julie Carr Smyth | Associated Press

Columbus, Ohio – A Democrat is within striking distance of winning a congressional race in Ohio on Tuesday for an open seat that has been reliably Republican for more than three decades. Both national parties are focusing on the contest for clues to whether Democrats will retake the U.S. House in November.

Republican President Donald Trump and Vice President Mike Pence have campaigned in support of the GOP candidate over the past week. Polls taken by Emerson College and Monmouth University before Saturday’s Trump event in suburban Columbus showed the race neck-and-neck.

Troy Balderson, a two-term Republican state senator, is working to retain GOP control of the 12th District. He faces Democrat Danny O’Connor, the Franklin County recorder, whose fundraising outpaced Balderson’s during the most recent reporting period by nearly four times.

Working phones at a volunteer site Monday, Balderson said he’s felt enthusiasm throughout the district following Trump’s visit Saturday.

“He definitely brought major excitement, and they were excited to see him up here,” Balderson said.

The seat was held for 18 years by GOP Gov. John Kasich and nearly another 18 by U.S. Rep. Pat Tiberi, a pro-business, establishment Republican. Both are backing and campaigning for Balderson in Tuesday’s special election for the remainder of Tiberi’s unexpired term.

Balderson, 57, is a Trump supporter but also is aligning himself with Kasich, who’s an outspoken Trump critic. He rebuffed questions about whether appearing with Trump might have cut into the popular governor’s influence in bringing out voters in Kasich’s home district.

“I had the president of the United States here on Saturday, and to stand on stage (with him) was incredible,” he said.

O’Connor, 31, also has taken care not to criticize Kasich. The Republican governor’s statewide popularity remains high, in part, because of an increase in support among Democrats as he’s maintained a steady barrage of negative commentary about the president.

The candidates made their final push Monday at stops around the central Ohio district, which sprawls from the urban, heavily Democratic Franklin County, home to Columbus, into Trump-supporting suburban and rural areas stretching east to Zanesville and the Appalachian foothills.

O’Connor’s candidacy is the latest barometer ahead of a November midterm election in which Democrats need 23 additional seats for a majority in the House. Democrats are being careful to manage expectations, pointing to Trump’s 11-point margin in the district two years ago as they try to hedge against a loss that could dampen their overall enthusiasm.

But Democrats have managed double-digit swings in special congressional elections in heavily GOP territory since Trump took office. Pennsylvania Rep. Conor Lamb in March flipped a Pittsburgh-area seat that Trump had won by nearly 20 points.

For Republicans, a convincing Balderson win could give the party ammunition to mock any forecast of a Democratic wave in November. It would also raise questions as to just how much of a battleground GOP-run Ohio still is.

Associated Press Writer Bill Barrow contributed to this report.