Voters headed to the polls Tuesday to decide the nationally watched election to represent Atlanta’s northern suburbs in Congress, a bitterly-contested vote between Republican Karen Handel or Democrat Jon Ossoff.

The race is much more than a vote to fill out the remainder of former U.S. Rep. Tom Price’s term after President Donald Trump’s tapped him to be health secretary. Both parties have poured unprecedented resources into the 6th District race — the cost now tops $50 million — and both see it as a chance to send a message to the American electorate.

Democrats hope an Ossoff victory could deal a blow to Trump's presidency and the GOP agenda, while giving other candidates a path to flipping more conservative strongholds. Republicans see a Handel win as a chance to bolster incumbents in competitive districts who are nervous about allying with Trump.

The contours of the race have been shaped for weeks. Once an insurgent outsider running against a corrupt political system, Handel casts herself in this contest as an experienced politician and traditional conservative with deep roots in the district.

And Ossoff, a former congressional aide and political newcomer, has centered his message on two audiences: There’s left-leaning voters infuriated by Trump and eager to elect a fresh-faced Democrat. And there’s the moderates and independents who have backed GOP candidates but are turned off by national politics.

The rollicking race has been filled with twists and turns, and there is no shortage of wild cards as the race hurtles toward an end. Polls show the race neck-and-neck, and analysts say it’s too close to call.

Here are a few factors that could decide the vote:

AJC reporter Greg Bluestein answers questions and discusses what he'll be watching as the votes are counted in Georgia's 6th District runoff between Jon Ossoff and Karen Handel.

The strongholds:

Stretching from east Cobb County to north DeKalb County, the district was drawn to favor Republicans. But Ossoff has tried to change the electorate by attracting first-time voters and others who don’t traditionally cast ballots in special elections.

He’s looking to run up the margins in the bluest parts of the territory, building on his April 18 turnout. He won a swath of land that extended through nearly all of north DeKalb to much of Sandy Springs, then darted up the Ga. 400 corridor before veering into parts of eastern Johns Creek.

Those territories are some of the most diverse parts of the district, and Ossoff’s campaign has targeted many of those voters with repeated mailers, phone calls and knocks on the door. An Atlanta Journal-Constitution poll of likely voters found that a majority of respondents were contacted in-person by his campaign.

Handel is focusing her final message on her core supporters: the conservatives who helped Price win one landslide victory after another since he won the seat in 2004.

That means winning big margins in east Cobb, the conservative stronghold that helped launch the careers of Newt Gingrich and Johnny Isakson, as well as her hometown of Roswell and the deep-red city of Milton in the extreme north of the district.

“This is uncharted territory analytically. The extremely high turnout, the uncertain political environment,” Ossoff said. “It’s is a neck-and-neck race.”

The turnout:

Turnout is set to far exceed the roughly 190,000 people who cast a ballot in the first round of voting in April, and some analysts expect the overall voter totals to top 250,000.

What such an eye-popping turnout means for both camps is unclear.

Mark Rountree of the pollster firm Landmark Communications sees a “bell curve” in the works. Smaller-than-expected turnout helps Ossoff, he said, because his voters tend to be more enthusiastic. A huge swell of participation could help him, too, because that likely means younger voters are turning out.

But he said there’s a “sweet spot” for Handel with a more traditional level of turnout in the middle of those two extremes. And a surge of turnout could wind up helping Republicans simply because they outnumber Democrats in the district.

Another wild card: Weather forecasts show scattered storms throughout the day, which could mean that some less-enthusiastic voters sit it out.

The early voting:

In the first round of voting, Ossoff won a commanding majority of the early vote — propelling him to nearly win the U.S. House seat outright over a scattered GOP field.

In the runoff vote, analysts from both sides of the aisle say Republicans have eaten into Ossoff’s advantage and that the early-vote outcome should be much tighter.

Ossoff is still expected to have the edge, but just how wide the margin is could determine the race. After all, the majority of voters in the district have already cast their ballots: More than 140,000 people cast early ballots — including nearly 40,000 people who didn’t participate in the April vote.

Handel said her campaign has been “very competitive” in early voting and that Ossoff was “unable to replicate what he did” in April. But Ossoff’s supporters say they’re reaching deep into a universe of people who rarely vote in special elections — or any election at all — to help drive their numbers.

The Trump factor:

By now, the dynamics are familiar to any 6th District voter: Trump barely carried the district in November, and his approval ratings are weak across the area, giving Democrats hope they can flip the district.

Ossoff launched his campaign with tough anti-Trump talk but has emphasized a more moderate message; Handel embraced Trump and his top priorities while saying she won’t be an “extension” of his White House.

Just how much will Trump factor into the outcome? The president has sent a flurry of tweets and robocalls supporting Handel’s campaign. But she’s also allied with other GOP leaders, including House Speaker Paul Ryan and Georgia Gov. Nathan Deal.

Ossoff has tried to hone in on Republicans frustrated with Trump. Mailers vow he’ll “stand up” to the president while he talks of how both parties are “complicit” in wasteful spending.

The reason for the dual-track messaging: He needs at least 10 percent, perhaps as much as 15 percent, of GOP voters to back him. And if he doesn’t win over enough GOP support, he might be in for a long night.

The shooting:

The race took a tenser turn after the ambush of U.S. Rep. Steve Scalise and other Republican legislators at a baseball field in suburban Washington.

Handel and several neighbors received a threatening letter with a white powder later deemed to be non-hazardous by the FBI. Ossoff hired a security detail amid a spate of unspecified threats targeting him. Both condemned an attack ad by a fringe GOP super PAC that sought to politicize the attack.

It’s uncertain whether the shooting will help shore up votes for either candidate, but a WSB poll released Monday showed a majority of voters who had yet to cast their ballots said they had no effect on their decision.

About one-third of election-day voters said the attack would make them “more likely” to cast their ballots, and most of those were Republican.


ELECTION DAY COVERAGE

Republican Karen Handel and Democrat Jon Ossoff face each other in a runoff Tuesday to fill the congressional seat Tom Price vacated to become secretary of health and human services.

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