By QUINN SCANLAN, ABC News

(WASHINGTON) — Control of the Senate for the first two years of President-elect Joe Biden’s administration hinges on the dual runoff elections taking place in Georgia on Tuesday.

Democrats need to win both seats in order to have a majority in Congress’ upper chamber — with the vice president-elect serving as the tie-breaking vote — and despite the state’s electoral history favoring Republicans, both matchups are expected to be decided by narrow margins, leaving the door open for a post-election period similar to the one that is still playing out after the general election: where one party is angry over the outcome, how the election was conducted and continually contesting the results.

More than three million Georgians have voted in this election, which is already a record for a runoff, and the secretary of state expects over one million more voters to the polls on Tuesday. Hundreds of millions of dollars have been raised and spent in support of or against the candidates: Republicans Kelly Loeffler and David Perdue — the incumbents — and Democrats Rev. Raphael Warnock and Jon Ossoff.

In the final days of a nationalized, two-month runoff campaign that’s taken place exclusively in the aftermath of an election that President Donald Trump and his allies have wrongly, but repeatedly, alleged was “rigged,” some of the biggest names from both sides of the political aisle have put their weight behind the candidates, helping to drive home their closing messages and convince supporters to return their absentee ballots or head to their precinct to vote before polls close at 7 p.m. on election day.

Former President Barack Obama appeared in an Ossoff ad launched in the final week of the campaign and former first lady Michelle Obama recorded a robocall and radio ad for Warnock. On Monday, Biden will campaign with Ossoff and Warnock in Atlanta, and Vice President-elect Kamala Harris headlined a drive-in rally for the Democratic candidates in Savannah, Georgia, on Sunday.

“Everything is at stake,” Harris said. “Savannah, you have a decision to elect two United States Senators. That is the power that is in your hands, to elect two individuals who are outstanding leaders, in Raphael Warnock and Jon Ossoff.”

Democrats hope to defy history, as Republicans paint grim picture of what that would look like

Democrats, riding off an electoral high after securing the state’s 16 electoral votes for the first time since 1992, feel that absentee and early voting returns show the momentum is on their side, but recognize that election day turnout will likely favor Republicans.

Throughout their campaigns, both Ossoff, a media executive and investigative journalist, and Warnock, the senior pastor at the historic Ebenezer Baptist Church in Atlanta, have focused on the most pressing problem Americans currently face — the health and economic impact of the coronavirus pandemic. They’ve criticized Perdue and Loeffler over well-timed stock trades made throughout the pandemic, which the Republicans have denied wrongdoing, and accused them of working for their own interests, instead of the American people’s, as senators who had a stake in negotiating a second coronavirus relief package.

Ossoff has branded the pair the “Bonnie and Clyde of political corruption in America” in his stump speech.

Meanwhile, Loeffler and Perdue have labeled the Democratic duo “radical socialists” or “radical liberals,” saying winning their races is the last line of defense against a party they say will try to fundamentally change America.

In attacking Ossoff, Perdue has zeroed in on China, accusing the 33-year-old of having ties to the Chinese Communist Party. The accusation stems from reporting by the National Review on payments his company received from PCCW Media Limited, a Hong Kong-based telecom company whose owner has spoken out against the region’s pursuit for democracy. Ossoff didn’t disclose the payments before the primary, but his spokesperson told the National Review that the money was compensation for the airing of two investigations produced by Ossoff’s company.

In the final stretch of the campaign, Loeffler started attacking elements of Warnock’s personal life and past, in addition to her attacks on past sermons he’s given at the pulpit, to push a narrative that Warnock is unfit for office. In one video that she, and other Republican elected officials supporting her, have repeatedly gone back to is of Warnock saying, “No man can serve god and the military.” Loeffler has said this rhetoric shows Warnock is “anti-American,” and anti-military, but Warnock has shot back, saying, “I think it’s unfortunate, and shameful, that they’re trying to distort not only my message, but the message of scripture.”

Republicans are a man down after Perdue was forced to quarantine after coming in “close contact” with a member of his campaign who tested positive for COVID-19. Perdue, who is currently a former senator because his regular term ended at noon on Sunday, tested negative for the virus, but still shifted his campaign strategy, doing interviews from home and participating in events virtually.

The party has filled the void on the campaign trail, though, with visits from top GOP surrogates like former Energy Secretary and former Texas Gov. Rick Perry, Sen. Lindsey Graham of South Carolina, Sen. Ted Cruz of Texas and Secretary of Agriculture Sonny Perdue, the former senator’s cousin, who served two terms as Georgia’s governor.

“We’ve got a chance here in a few days, to make sure that the most radical agenda in the history of American politics dies in the U.S. Senate, that anything coming out of Pelosi’s House comes to the Senate and we kill it dead,” Graham told a crowd of supporters at a concert rally on New Year’s Eve. “This is the most radical ideology we’ve faced as a nation. Both Democratic nominees have drunk the Kool-Aid. They really believe and they’ll be in lockstep with a socialist agenda that’s gonna come out of the House, but we’re gonna kill it dead here in Georgia, aren’t we?”

Graham spoke to the overarching message the Republican candidates’ campaigns and the party have been pushing from the start — that they must win their races so the Senate is a GOP “firewall” against Biden’s agenda. Democrats maintained control of the House of Representatives after the November election, but their majority is much slimmer than the one they’ve had for the last two years of the Trump administration.

GOP narrative of a “rigged” election spark turnout concerns

Both Vice President Mike Pence and Trump will travel to Georgia Monday to campaign for Loeffler and Perdue, events intended to fire up Republican voters before Tuesday.

“President Trump was here earlier this month, he’s coming back because you know why? He needs you to get out and vote. You have to exercise your right to vote. That’s exactly what he said. The country is counting on us,” Loeffler said at a recent rally. “I need you to call five friends, family members, co-workers, frenemies — whatever. Five calls or texts today about voting will keep the liberals away. That’s right. Five calls a day keeps the liberals away.”

But hampering Republicans’ efforts to get out the vote is the false, baseless narrative that rampant election fraud is the reason Trump lost. The president and his allies continue to perpetuate this baseless idea, and spread conspiracy theories about the election, even though their claims lack real evidence, which have been repeatedly disputed and outright debunked. State and local election officials and courts across the country, including in Georgia, have dismissed GOP-led lawsuits contesting the election.

Trump did it again on Saturday in an hour-long phone call with Georgia’s secretary of state, Republican Brad Raffensperger, which ABC News obtained audio of. In between spewing conspiracies about the election, Trump repeatedly demanded that Raffensperger “find” enough votes to overturn the election so that he is the winner. The secretary, who supported the president’s reelection, told Trump what he’s now said numerous times publicly: “We believe that we do have an accurate election.”

A week out from the election, a longtime GOP strategist based in Georgia, who requested anonymity in order to speak candidly about the races, told ABC News that even though Republicans have fared better in Georgia’s runoff elections — Democrats haven’t won a statewide runoff in the last 30 years — the national attention on the election and false claims, especially from the president, about the election are giving Democrats a better shot.

“Historically in the state of Georgia, runoffs tend to lean more Republican because you have a lower turnout, and, you know, not everybody’s paying attention. Well, this is a completely different scenario where this race is the only one in the country, hundreds of millions of dollars are being poured into the state, and you’re seeing a significant turnout in historically Democrat areas,” the strategist said. “This is an entirely get out the vote effort, and as it stands today, Democrats are winning in absentee ballot chasing and Democrats are winning in terms of early voting numbers. So, it’s very likely you see a very close race, or that these two Democrats have already won.”

Citing the secretary of state’s published data on early and absentee voting turnout, the strategist added: “At the end of the day, all of this narrative that you can’t trust the voting machines, you can’t trust absentee ballots — it’s hurting Republican turnout. So if you can’t trust the vote, how do you vote? And that’s the big question Republicans have right now.”

When the president headlined a rally for the senators in early December, he spent more time lambasting his own electoral loss and spreading disinformation about the November election than he did touting Loeffler and Perdue. His focus on the November election, specifically in Georgia, has only increased ahead of this critical election.

Friday evening, the president, who has nearly 90 million followers on Twitter, tweeted that the general election and the two senatorial runoff elections are “both illegal and invalid.” It wasn’t even a full 24 hours later when he urged supporters to “GET READY TO VOTE ON TUESDAY!!!” in the election he had just labeled “illegal and invalid.”

And during his call with Raffensperger Saturday, Trump himself acknowledged that supporters may be sitting out the election, though he asserted Raffensperger was to blame.

“You have a big election coming up … and because of what you’ve done to the president, a lot of people aren’t going out to vote. And a lot of Republicans are gonna vote negative because they hate what you did to the president,” Trump said.

In the two months since the general election, Raffensperger’s office has overseen two complete recounts of the votes in the presidential election, including an unprecedented hand count audit of the nearly five million votes cast in the race. He’s repeatedly reaffirmed that Biden was the legitimate winner of the election and has earned Trump’s ire because of it.

Even while conceding that illegal votes were likely cast and counted — as they are in every election — Raffensperger and other officials in his office have maintained that they have not found evidence of widespread voter fraud that would change the outcome of an election Trump lost by about 12,000 votes. Citing that a specific allegation was raised that Cobb County did not do signature matching for absentee ballots properly in the June primary, Raffensperger’s office launched a signature match audit in the county. Done in coordination with the Georgia Bureau of Investigation, the audit examined the signatures on around 15,000 absentee ballot oath envelopes, and upon completion, the GBI said investigators found only two instances where ballots should have gone through the “cure” process, but determined that even those ballots were not fraudulently cast.

But the public pleas from the Republicans overseeing the election, and other former elected officials — including former Sens. Saxby Chambliss, whom Perdue succeeded, and Johnny Isakson, whom Loeffler was appointed to replace — for the party to focus its energy on winning the runoff elections, Trump has stood by his fictional narrative of election fraud, and Loeffler and Perdue have stood staunchly behind him as he has, including calling for Raffensperger’s resignation not even a week after the general election.

Charles Bullock, a professor at the University of Georgia and an expert in Southern politics, told ABC News the senators basically have no choice but to stand by Trump, saying the president’s “antenna for identifying betrayers is particularly active right now.”

If races are as close as polls suggest, knowing winner on election night unlikely

While all votes must be cast by 7 p.m. Tuesday, it’s likely to be days before Georgians — and the rest of the country — know who’s won the runoffs. It all depends on how tight the races are, and according to FiveThirtyEight’s polling averages, the races are essentially deadlocked: Ossoff’s leading by about one percentage point and Warnock is leading by about two.

Asked when to anticipate significant results, Georgia’s Deputy Secretary of State Jordan Fuchs told ABC News, “Hopefully, we will have results two days after the election. It’s 100% dependent on counties, who run elections, so while we might do all the public relations in the world to get the counties to count faster, you know, counties determine how quickly they’re going to work.”

ABC News reached out to the state’s six largest counties, which all lean Democratic and will be critical to Ossoff or Warnock securing a victory in Georgia, to ask about their vote-counting plan and expectations. Contacted by ABC News multiple times over several days, a spokesperson for Fulton County, the largest in the state and home to most of Atlanta, said she would follow up with the elections staff but ultimately did not send details before this story was published. Similarly, a spokesperson for Gwinnett County, the second largest in the state, responded to ABC News’ inquiry and said he would follow up, but then did not send vote-counting details ahead of publishing. The elections department for Clayton County, the most Democratic county in the state that was responsible for the vote drop that put Biden ahead of Trump after the general, did not respond to emailed requests for details.

Counties were able to start processing returned absentee ballots up to the point of tabulation, which cannot happen until polls close, beginning 15 days before the election. The State Election Board, which passed this emergency rule ahead of the general election in an effort to speed up the vote counting, amended the rule for the runoff to require counties to begin doing this eight days before the election.

Ross Cavitt, a spokesperson for Cobb County, which is the third-largest in the state, said the county started processing absentee ballots the first day they legally could. On election night, he said the elections division plans to upload all votes cast during the early voting period and in-person on election day, as well as all absentee ballots returned before Tuesday. A spokesperson for DeKalb County, the fourth largest in the state, told ABC News the county also expects to upload results from advance voting, election day and “a large majority of absentee ballots.” Russell Bridges, the elections supervisor in Chatham County, where Savannah is located, told ABC News that if the runoff goes similarly to the November election, the advancing voting ballots will be uploaded early on election night, followed by absentee ballots scanned ahead of election day and then votes cast at polling places on election day. This all happened by around 11 p.m. on Nov. 3.

Despite backing the president’s false election claims and GOP-led legal challenges seeking changes to the absentee ballot process ahead of the runoff failing in court, Perdue has said he thinks the runoff election will be fair.

“Well, certainly it’s going to be a tight election. … If we get our vote out on Monday, I’m convinced now with 8,000 poll watchers and we’ve got cameras on all the drop boxes, we’re going to have as fair of an election as we can,” Perdue said on Fox News Friday. “In terms of January, I’m convinced that we have plugged a lot of the holes that might have been there in November.”

Raffensperger said that his office is prepared to oversee another recount if necessary. If the margin between the winning and losing candidate in either race is less than 0.5%, the losing candidate can request a machine recount, as the Trump campaign did after the general election was first certified on Nov. 20.

“We know we can do a recount if we have to. We can do another hand recount or we can do that also with the machine if the race gets that close,” Raffensperger told ABC’s Good Morning America Sunday.

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