Jon Ossoff, the Democratic candidate for Georgia's 6th Congressional District, speaks to supporters during an election-night watch party Tuesday. He will face Republican Karen Handel in a runoff June 20.

DUNWOODY, Ga. — A Georgia congressional election in a historically conservative district is headed to a runoff that raises the stakes in an early measure for President Donald Trump and both major parties ahead of the 2018 midterm elections.

Democrat Jon Ossoff, a 30-year-old former congressional staffer, fell a few percentage points shy of an outright victory amid an 18-candidate scramble in Georgia’s 6th Congressional District. Republican Karen Handel, a former Georgia secretary of state, finished a distant second, qualifying for the June 20 runoff.

The winner will succeed Republican Tom Price, who resigned the seat to join Trump’s administration as health secretary. But the matchup in greater Atlanta’s northern suburbs is just as much about Ossoff and Handel acting as proxies for the nation’s roiled political atmosphere.

Leaders in both major parties agree the race offers a prime test run for 2018 elections, because the affluent, well-educated Georgia district is replete with the kind of voters Democrats must attract to reclaim a House majority and win more gubernatorial and Senate races.

For Democrats, Ossoff’s near win in such a district — a Republican has held the seat since 1979, and Price won 62 percent of the vote in November — encourages the opposition movement that has flourished since Trump’s election. Yet falling short also highlights the party’s lingering power deficit in Washington and around the country.

“There is no doubt this is already a victory for the ages,” Ossoff said.

For Republicans, Ossoff’s strong performance acts as another wake-up call alongside a closer-than-expected win in a House special election last week in arch-conservative Kansas. It also serves notice that GOP candidates may always struggle to handle Trump’s polarizing effects.

Handel has treated Trump gingerly throughout, rarely mentioning him unless she’s asked and even then cautioning she isn’t a “rubber stamp” for anyone.

“I certainly support the president and will work with him where we agree,” Handel told The Associated Press at one of her final campaign stops before polls opened. “But my job ... is to be the representative for the people of the 6th District, and that’s what I believe regardless of who is the president.”