A tidal wave of advertisements. A field of 18 candidates all sharing the same ballot. A Democratic rising star who came from out of nowhere to threaten a GOP stronghold. And a string of irascible last-minute tweets from a president tuning into the race.

Those factors collided Tuesday for the special election to represent a suburban Atlanta district in Congress that has fast become the center of the national political debate. And as voters stream to the polls, the question of the night is bound to be whether Democrat Jon Ossoff can pull off an upset victory.

The polls opened at 7 a.m. across the district, which spans from east Cobb to north DeKalb, and they'll be open until 7 p.m.

Ossoff is gunning for a majority of the vote, a prospect that was unimaginable when he entered the race in January as a little-known investigative filmmaker who once worked for U.S. Rep. Hank Johnson. But an unprecedented fundraising haul and a jolt from President Donald Trump’s critics put him within striking distance.

"It's still within reach," Ossoff said. "Momentum is on our side. But special elections are unpredictable. And we're prepared for any outcome."

Once jittery Republicans sound increasingly confident they can keep Ossoff under 50 percent, thanks in part to a surge of attack ads from national GOP groups that depict him as an inexperienced stooge of U.S. House Democratic leader Nancy Pelosi. Data suggest that conservative-leaning voters kept pace with Democrats in early voting, and GOP campaigns say internal polls indicate a strong Election Day turnout.

“Tom Price’s win underscores just how truly Republican this district is,” Karen Handel, the leading Republican in many of the polls, said of Price’s victory in November with 62 percent of the vote. “You know how much I love football — the ball is in the air now.”

Add to this unpredictable mix last-minute tweets from Trump, who won Georgia by 5 points but carried the district by a narrower margin. The president referred to Ossoff as a “super Liberal Democrat” who would threaten his agenda on immigration and tax policy.

A Democratic victory in the district, which has been in Republican hands for decades, would be an epic rebuke to Trump's administration.

And his shadow looms large over the race, with some of the 11 Republicans in the contest running as an independent-minded check on Trump and others promising to be his staunchest ally in Congress. Three other leading Republicans — Bob Gray, Judson Hill and Dan Moody — have aimed fire at each other and Handel as much as Ossoff.

The Trump factor was on vivid display at a campaign stop Monday at a Roswell diner, where attorney Deborah McKinley had but one question for Handel: Did she vote for Trump? When Handel answered yes, McKinley sighed in relief.

“My main concern is finding the Trump loyalists who have the chance to win,” McKinley said after her encounter. “And I think she’s got the best shot.”

Trump is also energizing droves of left-leaning voters who want to hand his administration its first electoral defeat.

"He's a dark shadow. I despise Trump. I feel like he's a con man who has manipulated a lot of people," said Peggy Williams of east Cobb County. "And this is a way to send a message."

Ossoff’s best chance to win the contest might be Tuesday’s vote, when he can exploit the vicious Republican infighting. A June 20 runoff between the two top vote-getters looms if no candidate gets a majority of the votes, and Republicans would be pressured to unify behind a GOP candidate.

But Ossoff and his aides said his unprecedented $8.3 million fundraising haul and national attention to the race will keep him well stocked if the race drags into a second round.

More: A closer look at election-eve dynamics in the 6th District race

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