The polls close at 7 pm on Tuesday night in what may prove the most closely watched House special election in years — the race for Georgia’s Sixth Congressional District.

Democrat Jon Ossoff has emerged as the leader in a crowded field of 18 contenders vying to replace former Rep. Tom Price, now President Donald Trump’s health and human services secretary. Ossoff has raised more than $8 million, far more than any of the other candidates, and most polling — though notoriously unpredictable for special elections — pegs him at around 43 percent of the vote.

However, Ossoff isn’t just looking to get more votes than anyone else — he’s hoping to clear 50 percent of the vote total, which would allow him to avoid a runoff in June against the second-place candidate.

Doing that would probably require the leading Republican contenders — Georgia’s former Secretary of State Karen Handel and Bob Gray, a local council member and business executive — to see dramatic falls in GOP turnout from November’s election.

And that’s far from a sure bet.

“It becomes a huge deal if [Ossoff] actually wins outright — then you can say, ‘Wow, there really is something to this political strength of this resistance here,’” said Charles Bullock, a political scientist at Georgia State University, in an interview on Monday. “But if he gets a little over 40 percent and fails to clear the runoff, that’s a good showing for the Democrats but not particularly extraordinary.”

Who is running?

Georgia’s congressional races operate by what’s called a “jungle primary”: They’re open to all parties, and if any one candidate wins more than 50 percent of the vote (which for this race happens on April 18), then that candidate takes the seat outright.

But if nobody clears the 50 percent threshold, then the two candidates who got the most votes — regardless of party affiliation — advance to a second round, held for this race on June 20.

The possibility of making it to a runoff has led 18 candidates — 13 Republicans and five Democrats — to enter the race.

Ossoff is the only Democrat to poll above single digits. The 30-year-old is a former congressional aide and campaign manager for Rep. Hank Johnson (D-GA), who represents Atlanta. On the trail, Ossoff talks of staffing national security issues for Johnson and his degree from Georgetown University’s School of Foreign Service, but the Georgia GOP has tried to paint him as something of a frat boy.

A $1.1 million Star Wars–themed TV ad buy from a GOP Super PAC depicts him playing beer pong and dressing as Han Solo in an attack on his “experience.” Ossoff also does not live in the district, which Republicans have mentioned in attack ads against him.

Handel and Gray, the leading Republicans, have both been polling at around 15 percent. Handel is widely viewed as the candidate of the Republican establishment — she has been endorsed by the state Republican Party’s campaign chair, as well as Sandy Springs Mayor Rusty Paul and former US Sen. Saxby Chambliss.

Gray, meanwhile, has tapped into the more fiercely conservative voters in the Georgia Sixth. The Club for Growth, a conservative advocacy group, has launched an ad campaign against Handel, trying to denounce her as “big-spending career politician” due to her record as secretary of state.

Gray has also tried to position himself as the candidate to help President Trump “drain the swamp,” launching attacks against Handel that could fracture the Republican electorate even if they can keep Ossoff below 50 percent.

“It’s time to stand with President Trump, and I intend to be a willing partner to move this country forward,” Gray said at a recent East Cobb gathering of Republicans, according to the Atlanta Journal-Constitution. “It’s time to drain the swamp.”

Why does this matter?

This district is not one Democrats would normally have any business seriously contesting. Republicans have held the district, mostly composed of affluent suburbs north of Atlanta, with ease since 1979. Newt Gingrich and Sen. Johnny Isakson (R-GA) both held the seat. It’s gone red by about 30 points in each of the past five races, including in 2016, when Tom Price won it in a landslide.

“It’s a gerrymandered, suburban, Republican district,” says Phil Lunney, legislative liaison for the Fulton County Democrats. “It’s a really hard place for us to win.”

But though they were crushed at the local level, something in November’s returns gave Georgia’s Democrats a cause for hope. In a dramatic swing from the past four presidential elections, Trump only won the Georgia Sixth by 1.5 points. (Mitt Romney won it by 24 points in 2012.)

Trump seems to have noticed, and he recorded a robocall that went out to voters in the district on Monday:

A loss today for Georgia Republicans, particularly after their party’s scare in Kansas earlier this month, would signal that the grassroots anti-Trump activism following the election could translate into real electoral success. And that’s something Democrats would be very eager to celebrate.

Correction: A previous version of this story misstated the poll closing time.