UPDATE: The race in Georgia’s 6th Congressional District is headed to a runoff. Polls concluded early Wednesday that Democrat Jon Ossoff was a few percentage points shy of the 50 percent of votes he needed for a clean victory in the race. He will head to a June 20 runoff with Republican Karen Handel, a former Georgia secretary of state. Read the full results here.

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A special election to fill a longtime Republican House seat in Georgia has turned into a national referendum on Donald Trump’s presidency, as well as an early test of the left’s ability to turn its opposition to Mr. Trump into electoral success.

The seat, which Republican Tom Price held for six terms before he became Trump’s Health and Human Services secretary earlier this year, has traditionally been an afterthought for the party. Republicans have controlled the district — which was held by Newt Gingrich, a former House speaker — since 1979. Price won re-election last year by 23 points.

But Trump only carried the district, which covers a swath of moderate suburbs north of Atlanta, by 1.5 points in 2016. Next week’s special election features 18 candidates. Jon Ossoff, the Democratic front-runner for the seat, is hoping to capitalize on Trump’s small margin of victory to score an upset win that would resonate nationwide with Republicans seeking re-election next year.

The 2016 presidential election “was a wake up call that Americans have lost faith in our political institutions,” Ossoff, a 30-year-old former congressional aide and documentary filmmaker, told PBS NewsHour in an interview.

Ossoff is leading his nearest competitor by double digits, according to polls, but is expected to fall short of the 50 percent needed to avoid a runoff. If none of the 18 candidates in the race — five Democrats, 11 Republicans and two independents — win a majority of the vote on Tuesday, the two top finishers will face each other in a June 20 runoff.

In a recent poll of likely voters, Ossoff came in first with 39 percent, followed by Republican Karen Handel, a former Georgia secretary of state, who finished second with 15 percent. The poll was conducted in the first week of April by the right-leaning polling form RHH Elections.

The Georgia race comes on the heels of a hotly contested special election in Kansas last week. James Thompson, a Democrat backed by a group tied to Sen. Bernie Sanders of Vermont, lost by seven points in a deeply conservative congressional district that Trump carried by 27 points in 2016.

The race, the first federal election since Trump’s victory last fall, was a sign of the growing energy among political groups on the left. Activists have staged marches and spoken out at town hall meetings with congressional lawmakers in the months since Trump took office, drawing comparisons to the conservative Tea Party movement that sprang up after Barack Obama’s election in 2008.

Donations from liberal donors and groups across the country have helped fuel the rise of a Democratic frontrunner.

In Georgia, donations from liberal donors and groups across the country have helped fuel Ossoff’s rise. Handel raised $463,000 through early April, campaign finance records show. Ossoff’s campaign raised more than $8.3 million through April 5, according to FEC filings. Of that, 95 percent has come from donors outside of Georgia.

“The excitement levels we’re seeing right now are unprecedented,” Rebecca DeHart, the executive director of the Georgia Democratic Party, said. Democrats see the race as “a referendum on the Trump administration,” she added.

The energy on the left, coupled with the party’s strong showing in Kansas, has put pressure on Republicans to deliver in Georgia. Another tight finish, or an outright loss, could set off alarm bells among GOP lawmakers, who are preparing for three more special elections this year. But the attention on the race has also raised expectations for Ossoff, a first-time candidate who has been suddenly thrust into the national spotlight.

“Ossoff has become the symbol of the resistance” on the left in Georgia’s Sixth Congressional District, said Tharon Johnson, a Democratic strategist based in Atlanta.

Becky Arrington, 63, a voter who lives in the district and considers herself a member of the liberal opposition, said she was jolted by Trump’s victory. “After the election I was stunned for a while,” she said.

For Arrington and others in the district, the special election has offered an opportunity to convert pent-up frustration into electoral action. Arrington said other steps, like lodging complaints with a politician’s office, haven’t gone far enough.

“How many times can we call a senator?” said Arrington, who has hosted a training session for phone banking and canvassing, as well as a question and answer session for Ossoff, at her home.

“People are really coming out and are pretty brazen” in support of Ossoff, she said. “They aren’t alone and they do have a voice.”

Despite an emboldened Democratic base, conservatives in the state remain bullish about their chances of winning the special election.

“Georgia Democrats are desperate to find some relevance after being beat in November,” said Ryan Mahoney, the spokesman for the Georgia Republican Party.

“Georgia Democrats are desperate to find some relevance after being beat in November.” —

Ryan Mahoney, Georgia GOP spokesman

“I’m still a little baffled at the positive outlook the [Democrats] have on this,” said Seth Weathers, a Republican consultant who served as the Trump campaign’s state director in Georgia.

But in an election that was supposed to be a sure thing for the GOP, the Republicans vying for Price’s seat have had trouble differentiating themselves from the pack. Mahoney said the field of 11 GOP candidates signaled the party’s strength in the district, and “reflects the excitement in the electorate for a race like this in an off-election year.”

In a phone interview, Judson Hill, a former Republican state senator who is in the top five in polls, cited his “strong record of being a fiscally conservative leader in the state.”

Handel, the Republican frontrunner, also cited her experience as a state official. Washington is “a climate where we need individuals” who know how to govern, Handel told the NewsHour. “That’s very suited to my skillset.”

Other Republicans in the race have focused on their outsider status.

Bob Gray, a business executive who served briefly on the Johns Creek City Council, has not shied away from drawing parallels between himself and Trump, who touted his business acumen and lack of political experience on the campaign trail last year.

Gray said he did not consider running for state or federal office until Trump was elected. Now, “I’m running to save the American dream,” he said in an interview. “I don’t recognize the country anymore.” Further echoing Trump’s campaign rhetoric, Gray said his candidacy “has threatened the political establishment” in the state.

But Republicans in the race have been divided on whether to tie their candidacy to Trump and his policies.

Soon after taking office, Trump had the highest disapproval numbers of any new U.S. president in the history of modern polling, according to a CNN/ORC poll. More recent numbers show Trump’s approval rating remains low, at 39 percent. The White House has been distracted early on by several investigations into ties between Russia and Trump’s campaign. And the Trump administration and Republican-controlled Congress have also suffered setbacks on immigration and health care.

Given the tense political climate, some Republicans in the race have been wary to associate themselves too closely with Trump. As Hill put it, “the president is not on the ballot here.”

Ossoff has capitalized on the moment. When he announced his candidacy in early January, he promised to “make Trump furious.” Since then, Ossoff has made his attacks on Trump a central theme of his campaign.

The strategy appears to be working. Whereas in the race in Kansas, in a district Trump won by a large margin, Sen. Ted Cruz of Texas campaigned with the Republican candidate, and the president and Vice President Mike Pence recorded calls urging Republicans to vote, in the Georgia special election — a district where Trump only narrowly edged out Hillary Clinton — national Republicans have largely stayed away.

“If Donald Trump was so popular” in the area, said Johnson, the Democratic strategist, “Air Force One would have landed [here] a long time ago.”

Weathers, Trump’s 2016 campaign chief in Georgia, insisted Democrats were overconfident. Winning a seat held for decades by Republicans is a “pipe dream,” he said.

But in a sign of how seriously Republicans are taking the race, conservative groups like the Congressional Leadership Fund — a super PAC dedicated to protecting the party’s majority in the House — are spending millions of dollars in ad campaigns against Ossoff. One mailer from the Congressional Leadership Fund accused the Democrat of colluding with Osama bin Laden because he accepted money from broadcaster Al-Jazeera for a documentary film.

In his interview with the NewsHour, Ossoff called the attack ads “troubling” and said they reveal the “predictable cynical Washington operatives’ approach to politics.”

DeHart, the head of the Georgia Democratic Party, was more blunt. Republicans “are absolutely terrified,” she said. “If they didn’t think we had a shot, we shouldn’t see the funds coming in the state they way it is.”

As the race enters its final days, Democratic voters expressed cautious optimism. If nothing else, Arrington said, the campaign demonstrated that the political landscape has changed under Trump.

“All bets are off,” she said. “We can’t look at anything the same as we have in the past.”

Because of an editing error, an earlier version of this story misstated Ryan Mahoney’s position. He is the spokesman of the Georgia Republican Party, not the communications director of the Republican National Committee.