ALPHARETTA, Ga. (AP) — Republicans are bidding to prevent a major upset in a conservative Georgia congressional district where Democrats stoked by opposition to President Donald Trump have rallied behind a candidate who has raised a shocking amount of money for a special election.

Tuesday's jungle-style primary lumps all 18 candidates on one ballot and is expected to be more competitive than Republicans' single-digit victory in Kansas last week that also tested both parties' strategies for the 2018 midterm elections with Trump in the White House.

Trump underperformed other Republicans in the suburban Atlanta district, an affluent, well-educated swath filled with the kind of voters Democrats need if they hope to reclaim a House majority next year.

Republicans essentially concede that Democrat Jon Ossoff, a former congressional staffer, will lead Tuesday's voting. That leaves 11 Republican candidates hoping the 30-year-old investigative filmmaker fails to reach a majority. If he doesn't, Ossoff and the top GOP vote-getter would meet in a June 20 runoff.

Five Democrats will appear on the ballot, but Ossoff is the GOP's greatest threat. He raised more than $8.3 million, most of it from outside the district. Two independent candidates also are running. The winner will succeed Tom Price, who resigned to become Trump's health secretary.

Ossoff has enough momentum to draw attention from Trump himself. The president took to Twitter on Monday to blast the "super liberal" Democrat in the contest without naming names. He said the "super liberal" Democrat "wants to protect criminals, allow illegal immigration and raise taxes!" Trump, Ossoff answered in a statement, is "misinformed."

Both major parties have dispatched paid field staffers. Republican groups are running a blitz of ads trying to tie Ossoff to House Minority Leader Nancy Pelosi; a political action committee backed by House Speaker Ryan has spent more than $2 million.

Karen Handel, Georgia's former secretary of state, has led the Republican field. Technology executive Bob Gray; and two former state senators, Dan Moody and Judson Hill — are polling closest to Handel in a fight for the No. 2 spot.

The GOP scramble has been intense, with GOP rivals accusing Handel of being a political opportunist and the conservative Club for Growth spending six figures on ads to defeat her.

National Republicans say any of the four competitive GOP candidates could defeat Ossoff in a second round of voting. GOP voters, they predict, would be energized in a Republican vs. Democrat scenario, making it harder for Ossoff to run above the fray as he has leading up to the primary.

Ossoff has tried to walk a line between liberals looking for a chance to oppose Trump and Republicans who couldn't support him in November. Ossoff pledges to fight Trump when he "embarrasses" the country. But he tells voters in one ad, "I'll work with anybody in Washington who respects your tax dollars."

Handel is among the Republican candidates trying to maintain some distance from Trump, rarely discussing him unless asked.

Gray has instead tried to portray himself as a "willing partner" for the president. Other Republican candidates, though, have questioned whether Gray always backed Trump or is simply strategizing a path to a runoff election.

Polls will be open from 7 a.m. to 7 p.m.

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By KATHLEEN FOODY and BILL BARROW, Associated Press
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Follow Foody and Barrow on Twitter at https://twitter.com/KatieFoody and https://twitter.com/BillBarrowAP