Democrat Jon Ossoff and Republican Karen Handel are the candidates in the closely watched special election in the 6th Congressional District in Georgia. (EPA photos)

Democrats will turn their gaze south this week, hoping victory in a special election in Georgia’s 6th Congressional District will serve as a referendum on President Trump and spark their efforts to counter his agenda — and to win back the House.

Embodying those hopes is Democrat Jon Ossoff, a 30-year-old former Capitol Hill staffer who has campaigned as a moderate in the wealthy suburbs north of Atlanta and raised more than $23 million.

But despite Ossoff’s financial advantage — the showdown is the most expensive House race in history — Democrats remain on edge. Polls show the clash between Ossoff and Republican Karen Handel too close to call, and GOP candidates have prevailed in several special elections this year.

Timing is critical, with Tuesday’s vote coming as congressional Democrats are rousing their base by attempting to block Republican legislation to overhaul the nation’s health-care system. Senate GOP leaders have been privately revising a House-passed version for weeks, aiming to call a vote by the end of June.

Many Democrats see the Georgia race and their health-care moves as intertwined. If Ossoff wins, the likely wave of enthusiasm could rattle Trump and ­Republicans. If Ossoff loses, it could be demoralizing and reveal the challenges facing Democrats ahead of next year’s midterm elections, despite the GOP health-care proposal’s unpopularity and the controversy over Trump’s handling of investigations into Russian meddling in the 2016 presidential election.

Democrats need to flip 24 ­Republican-held seats to take back the House majority, which they lost seven years ago.

The stakes have stoked talk of unity among wings of the Democratic Party, which has dealt with intraparty tensions since Trump won.

On Sunday, Sen. Bernie Sanders (I-Vt.) said he was standing with Ossoff, even though ­Ossoff has not run as a vocal progressive.

“Oh, absolutely,” Sanders said on CNN’s “State of the Union.” “I very much want Ossoff to win. His views are a lot better than his Republican opponent’s.”

Sanders also said Democrats “should do everything possible” to counter Trump and the Republican health-care bill, and framed the Georgia race as one of the ways the party could begin to “turn around its fortune.”

Senate Democratic leaders are considering several maneuvers to stop Republicans from proceeding on the legislation and to protest the GOP’s behind-the-scenes discussions, according to aides.

Once senators return to Washington on Monday, Democrats may threaten to halt procedural routines and boycott committee meetings and hearings, the aides said.

Senate Republicans have acknowledged the potential political pitfalls should their legislation be defined by the secrecy in which it has been deliberated.

“The Senate is not a place where you can just cook up something behind closed doors and rush it for a vote on the floor,” Sen. Marco Rubio (R-Fla.) said Sunday on CBS’s “Face the Nation.”

“Every camera in the world is going to have to see what’s in it,” Rubio said.

Ossoff — who nearly won the seat outright in the first round of voting in April — spent the weekend urging Democrats who are furious with Trump to turn out, all while keeping his tone and message steady as he courted more centrist Republicans in a district that has been in GOP hands since 1979. It was represented by Health and Human Services Secretary Tom Price until he resigned to join Trump’s Cabinet.

“We have a great candidate,” Rep. John Lewis (D-Ga.), a veteran civil rights leader, said as he campaigned alongside Ossoff. “Smart, young and just good.”

Ossoff said Tuesday’s election would have consequences far ­beyond the district’s well-
manicured lawns and glassy ­office parks.

“Folks across the district, folks across the state, folks across the country, there are those who have lost faith,” Ossoff said. “All of us here today, and all of us in this district, have a chance now to help restore some of that.”

Ossoff has avoided making the Russia probes and Trump’s decision to fire former FBI director James B. Comey central to his closing pitch, calling for a vigorous investigation but mostly focusing on health care and the economy.

Handel, meanwhile, has embraced her long ties to state and local Republicans, a point she has played up repeatedly as she has jeered Ossoff for living outside the district.

A former Georgia secretary of state, Handel campaigned with Price and Agriculture Secretary Sonny Perdue, a former Georgia governor.

“This is a harbinger of national politics,” Perdue said Saturday at a Handel rally. “The world is looking, the nation is looking, and all the money has flowed in here.

“Don’t be fooled by someone who doesn’t have a record,” he added. “Let me tell you something, [Ossoff] is a puppet, and the strings are being pulled by the Democrats and Nancy Pelosi,” the House minority leader.

Early voting levels have been extraordinarily high, reflective of the intense interest in the race. More than 120,000 people have already voted, nearly a quarter of all registered voters in the district.

Trump’s shadow continues to loom, not so much because of Republican reservations about his policies but because of their unease with his combative persona and the lack of progress in enacting key priorities, such as tax cuts and the repeal of aspects of the health-care law.

Handel has turned to the president for a fundraising lift but otherwise treaded cautiously when speaking of him, aware that much of her well-educated conservative base does not always identify with his roaring populism.

Trump barely won the district last year as Price coasted to a double-digit victory.

At the weekend rally, Perdue noted that some Republicans “may even be turned off by our president.” But he urged solidarity and said Trump “keeps his promises.”

Handel has been cagey, too, on the Republican health-care plan, saying the House bill is far from perfect in a nod to concerns among voters about the legislation’s scope and its coverage of people who have preexisting conditions or rely on Medicaid.

On Russia, Handel has dismissed the mounting questions about Trump’s interactions with law enforcement officials as “noise” but said she supports letting “the facts take us where the facts take us.”

Handel has raised more than $5 million, putting her far behind Ossoff, but she has been boosted by outside groups that have spent more than $11 million on her behalf. A political action committee aligned with House Speaker Paul D. Ryan (R-Wis.) has been particularly active.

Ossoff’s droves of volunteers have drawn notice. During a recent trip to the district, The Washington Post encountered numbers of them in blue T-shirts going door to door — a glimpse into the energy on the Democratic side, especially among progressive millennial-age voters who see Trump as anathema to their views.

Ossoff said Friday on MSNBC that he has built a coalition of “Democrats, independents and Republicans.”

But as she stood Saturday in front of an enormous American flag at an airport hangar, Handel described Ossoff as a liberal interloper who had values from “3,000 miles away in San Francisco.”

It was a return to traditional partisan themes, seemingly as a reminder to any Republican tempted to stay home or vote for Ossoff.

“We are going to show up on Tuesday, and we’re going to rock Nancy Pelosi’s world,” Handel said to cheers.