“We’re in a jump ball here,” Tom Perez, the chairman of the Democratic National Committee, said on MSNBC late Tuesday night.

Like the March special election in a Trump-friendly district in Pennsylvania and last year’s closely fought House race in Georgia, both parties spent millions to win a seat that will, for the moment, have little impact on the balance in power in Washington, D.C. Balderson’s win earns him a congressional tenure of just five months; he will have to defend his seat against O’Connor again in three months.

But election forecasters said this race likely provided the cleanest test yet of whether the Democratic enthusiasm edge in 2018 could carry the party into the House majority this fall. Trump won the district, which spans from Columbus into rural Ohio, by 11 points in 2016. Its previous representative, Pat Tiberi, was a reliable Republican vote who served nine terms and never won by less than nine percentage points—the margin of his first victory in 2000. Voters there have not sent a Democrat to Congress since 1980. And the electorate features plenty of the college-educated, suburban voters likely to be disenchanted with Trump, who Democrats are counting on to support them across the country.

‘We are in a Trump-driven worst-case situation right now’

If Democrats could win a GOP district like Ohio’s 12th, in other words, they could easily pick up the 22 other seats they’ll need to win the House. And even if they fell just short, as O’Connor did on Tuesday, a tight margin would portend a difficult path in the fall for Republicans. A memo that the Democratic Congressional Campaign Committee sent to reporters before polls closed noted that there were 79 GOP-held seats across the country that the party considered more winnable targets in November.

For all those reasons, Republicans went all out in the closing days to push Balderson over the line. Trump flew in for a rally in which he attacked “Danny Boy” O’Connor as a tool of House Democratic Leader Nancy Pelosi and sought to gin up his base to turn out for Balderson. Despite being no fan of Trump’s, Ohio’s Republican governor, John Kasich, cut an ad backing Balderson, and GOP-backed groups outspent Democrats by a significant margin in the final weeks of the campaign.

Conservatives took the win on Tuesday night, but the nail-biter left them with little to celebrate. “While we won tonight, this remains a very tough political environment,” said Corry Bliss, the executive director of the Congressional Leadership Fund, the main House GOP super PAC, in a statement. “And moving forward, we cannot expect to win tough races when our candidate is being out-raised.”

Trump made a similarly late entry into Pennsylvania’s closely fought House special election in March, when the Democrat Conor Lamb defeated the Republican Rick Saccone by fewer than 1,000 votes in a district the president won even more handily in 2016. This time around, it wasn’t clear whether Trump’s intervention had succeeded in waking up Republican voters, firing up progressives, or both. A day before landing in Ohio, the president insulted the intelligence of the state’s hometown star LeBron James in a tweet that could have undercut his push for Balderson.