Georgia Senate elections live updates: Jon Ossoff projected to win Ga. Senate seat

Gabriel Sterling, the state voting system implementation manager, said in an evening election update that the largest portion of remaining uncounted votes is from DeKalb County, a heavily Democratic suburban Atlanta area.

"The biggest tranche of votes that exists out there in a single bucket right now still looks to be the advanced voting in DeKalb County," Sterling said. 

With 80% of the expected vote reporting in, GOP candidates Perdue and Loeffler are leading their races by small margins. 

Sterling said from the press conference in Atlanta that he wasn't aware of any issues that could delay the reporting but added, "It can be like seesaw for the rest of the evening."

Sterling said 64 of the state's 159 counties have completed reporting all votes.

-ABC News' Quinn Scanlan

Georgia Lt. Gov. Geoff Duncan, a Republican, told ABC News Live he's worried that President Donald Trump's baseless allegations of election fraud in the state "absolutely" might have depressed GOP turnout in the runoff races. 

"Unfortunately, too many folks in our party over the last two months have been talking about misinformation, election fraud and creating a distraction," Duncan said. 

"We've been outworked, out-focused, but my hope is that Kelly Loeffler's and David Purdue's hard work over the last two months is going to get them across the finish line and help us kind of regroup as a party here in this state, and also as a country, and be able to roll back out and get the White House in 2024," he added. 

ABC News Chief Congressional Correspondent Mary Bruce stressed the significance of Tuesday's runoffs, not only because they will determine control of the Senate but because they leave President-elect Joe Biden's agenda hanging in the balance. 

"It's not just how much he can get done but also the expediency with which he might be able to get things done," Bruce said, outlining big promises in Biden's agenda, from health care to climate change.

Biden has noted in recent days, while stumping for Democratic candidates, that if Democrats are able to win both seats, the $2,000 stimulus checks Democrats have been pushing for could happen immediately. Also, the approval of additional aid to state and local governments and resources to distribute the coronavirus vaccine in a more timely fashion could come quickly. 

"Not to say that Joe Biden's agenda would hit a complete brick wall if Republicans continue to maintain control in the Senate because, of course, Joe Biden prides himself on having a great working and personal relationship with Republican leader Mitch McConnell, but it certainly would make Joe Biden's agenda and his political ambitions here much, much, much easier," Bruce said. 

Bruce also noted how the expected efforts by Republicans to object to the certification of the Electoral College results on Wednesday could give the public a sense of the "uphill battle" Biden may face if the GOP does maintain control of the Senate.

The turnout of Black voters in Georgia’s runoff Senate races rose a percentage point from what it was in November, according to ABC News’ preliminary exit poll -- potentially a positive signal for Democratic candidates Jon Ossoff and Raphael Warnock.

The African American turnout is "a very encouraging sign for Democrats. It shows that they’re getting their base out,” ABC News Political Director Rick Klein said on ABC News Live.

Preliminary exit poll reporting shows that Black voters account for 29% of the electorate in Tuesday's race, up from 28% in November.

The exit poll data indicates that 93% of Black voters turned out for both Ossoff and Warnock.

"[African Americans are] as reliable of a Democratic bloc as there is and so far the Democrats look like they did their job in getting them to the polls," Klein said.