By most metrics, Danny O’Connor, the Democratic nominee to replace retired Congressman Pat Tiberi, is a long shot. His Republican opponent, Troy Balderson, enjoys the support of the state’s governor, John Kasich, and of President Donald Trump. That should carry weight in a gerrymandered district like Ohio’s 12th, which has voted Republican for around 40 years and went for Trump in 2016 by 11 points.

But O’Connor, the 31-year-old recorder for Franklin County, has unexpectedly tightened Balderson’s lead, to the point that Larry Sabato’s Crystal Ball shifted the race’s rating from “leans Republican” to “toss-up.” The Cook Political Report rates it likewise. Now, Trump himself is traveling to Ohio to stump for Balderson ahead of next week’s special election.

.@Troy_Balderson of Ohio is running for Congress - so important to the Republican Party. Cast you early vote or vote on August 7th. Troy is strong on crime and borders, loves our Military, our Vets and our Second Amendment. He has my full and total Endorsement! — Donald J. Trump (@realDonaldTrump) July 27, 2018

An unsettled GOP has invested heavily in the race. Politico reported on Tuesday that national Republicans “have bombarded the suburban Columbus district with more than $3.3 million in TV ads in an effort to boost Balderson, a state legislator,” though O’Connor maintains a fundraising lead of $1,445,504 to Balderson’s $1,264,723. That O’Connor has managed to shrink his opponent’s lead to this degree could portend other Democratic successes in November. (The New York Times called the race a “big test of the ‘blue wave.’”) But if he wins—or simply makes it close—he may also put the party’s leadership in a difficult position.

O’Connor repeatedly has said that he won’t support Nancy Pelosi as the Democratic leader in the House, a position he seemed to reaffirm in his final ad, released on Tuesday. “The same old politics in Washington just aren’t working. Democrats and Republicans are at each other’s throats every day, leaving the issues that matter most to your family behind. We need new leadership in both parties,” he said.

He’s hardly the only Democrat politician to oppose Pelosi. In 2016, she survived a leadership challenge from another Ohio Democrat, Representative Tim Ryan, and as Politico reported in June, 11 candidates on the Democratic Congressional Campaign Committee’s list of top-tier candidates have said they’ll oppose her as the party’s leader in the House. The opposition doesn’t map cleanly onto the party’s internal divisions, either. Some candidates, like Alexandria Ocasio-Cortez in New York, are left wing, but others aren’t. Ryan is a moderate who recently attended a conference organized by Third Way, the centrist think tank.