A Democrat aims to pull off an upset election victory in the US state of Georgia on Tuesday in a race seen as a popularity test for President Trump.
The congressional district has long been Republican, but Democrat Jon Ossoff has surged in opinion polls with a campaign billed Make Trump Furious.
The suburban Atlanta seat was left vacant when Congressman Tom Price left to join the Trump administration.
There are 18 candidates, including 11 Republicans, dividing their support.
Georgia’s sixth district has been held by Republicans since 1979, but the seat could now be up for grabs.
Republicans were spared humiliation last week when they narrowly defended a deeply conservative Kansas seat vacated when Mr Trump appointed Congressman Mike Pompeo to lead the CIA.
What’s a jungle primary?
There are 18 candidates running in the so-called jungle primary – including 11 Republicans and five Democrats – all on one ballot.
If no candidate receives more than 50% of the vote, the top two finishers compete in a runoff election on 20 June.
Only one candidate is close to claiming a simple majority: Mr Ossoff, a 30-year-old political newcomer who most recently worked as a documentary filmmaker after serving as a congressional aide to Georgia representative John Lewis.
Despite his lack of experience, Mr Ossoff raised a whopping $8.3m in the first quarter, making it one of the most expensive congressional races ever.
Analysis – by Rajini Vaidyanathan, BBC News
This seat, which takes in the well-heeled suburbs of Atlanta, is usually safe territory for establishment Republicans, like former occupant Tom Price. In November, Mr Price, who has stood down after 12 years to become US health secretary, won with 61% of the vote.
But Mr Trump didn’t win this district as decisively in the presidential contest – securing a margin of victory of only 1.5% of the vote.
If this race is seen through the prism of national politics – a referendum on the Trump presidency – it could spell trouble for the Republican party.
I spoke to several Republican voters in the district who said they’d deserted the party since November. Some said they’d voted for a Democrat for the first time to send a message to Washington.
If this race goes down to a runoff, much will hinge on which Republican candidate enters the final fray – whether it’s a Trump-supporting contender, or an establishment Republican.
What are the stakes?
If Democrats win the election outright on Tuesday, it would be a major embarrassment for President Trump.
It could spur Republican lawmakers in competitive districts elsewhere in the country to distance themselves from him ahead of the nationwide 2018 mid-term elections.
Democrats are hoping to capitalise on President Trump’s low popularity ratings, which currently stand at 40%, according to Gallup.
Sensing the danger, he attacked Mr Ossoff in tweets on Tuesday morning as a “super Liberal Democrat” who is “very weak on crime and illegal immigration, bad for jobs and wants higher taxes”.
Hollywood actor Samuel Jackson is among those who have urged Democrats to head to the polls.
“Remember what happened the last time people stayed home,” Jackson said in one commercial. “We got stuck with Trump.
“We have to channel the great vengeance and furious anger we have for this administration into votes at the ballot box.”
Democrats hope for upset victory in Georgia’s sixth district