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

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.

More than 3 million voters in the Georgia runoff elections cast their ballots early -- 1,018,381 by mail and 2,074,994 early in-person -- according to Georgia Votes, already a record-setting figure for runoff elections.

The total early vote so far also includes 123,079 who did not participate in November's general election -- which is 35,000 more votes than the margin that separated Sen. David Perdue and Jon Ossoff the first time around, when the incumbent Republican edged out his challenger by just over 88,000 votes. Sen. Kelly Loeffler and Raphael Warnock were competing in a jungle primary in which the large field diluted their vote shares.

The secretary of state's office won't have Tuesday's in-person turnout numbers until at least 1 p.m. on Wednesday when counties are required to report how many ballots they received Tuesday in order to calculate the number of outstanding ballots. It may take days for the final results to become available depending on how close the races are.

Republicans are relying on high Election Day turnout, believing close to a million votes on Tuesday is likely their path to victory. At a rally in Dalton on Monday night, President Donald Trump signaled how many votes Republicans are eyeing: "I guess we have to get over a million votes tomorrow, right, Kelly? Over a million. All right. That's a lot of votes, Kelly, but we'll do it."

-ABC News' Quinn Scanlan, Kendall Karson and Meg Cunningham

The results of the runoff elections will determine which party controls the U.S. Senate -- and voters are nearly split on their preference, preliminary exit poll results show.

Forty-nine percent prefer Republican Party control, while 48% prefer control by the Democrats, based on the preliminary results. 

The GOP needs either seat to retain control of the Senate, while the Democrats need both to win control. 

Voters also were nearly split in their vote for president in the general election, based on the preliminary results -- suggesting that Democrats were holding their own in runoff turnout. 

Voters in the race between Democrat Raphael Warnock and Republican Kelly Loeffler report having voted a dead-even 47%-47% Donald Trump-Joe Biden, preliminary results show. In the contest between Democrat Jon Ossoff and Republican David Perdue, it’s about the same -- 48%-47% Trump-Biden, based on preliminary results.

-ABC News' Gary Langer, Christine Filer and Steven Sparks