That means Georgia, which is also still counting ballots in a neck-and-neck presidential race expected to go to a recount, is shaping up to be ground zero for whether Congress will be divided again next year.
"All eyes will be on Georgia for the next two months," Emory University political science professor Andra Gillespie said. "There will be record spending, unprecedented campaigning and tons of mudslinging in these races — more than what we're used to seeing."
Currently, Republicans hold a 53-47 majority in the U.S. Senate. With several races undecided, Democrats have gained one new seat in the Senate but would need two more for a 50-50 split. Then, if Joe Biden wins the White House, Kamala Harris as vice president would cast tiebreaking votes in the chamber.
A narrowly divided Senate, regardless of who is in control, means whoever is president will need cross-party cooperation in many cases to move any significant legislative priorities forward. Democrats will retain their majority in the House of Representatives but have a smaller margin.
For now, final calls need to be made in two other pending Senate races in North Carolina and Alaska. Republicans in both cases said they are confident they will pull out wins, making a Democratic sweep of both Georgia races the only path left for Democrats to gain the majority.
Senate Majority Leader Mitch McConnell, R-Ky., said he isn't sure if he'll keep his job, or if Minority Leader Chuck Schumer will move into that leadership slot. However, McConnell noted that Republicans outperformed pundits' expectations that the GOP would lose Senate control outright with the November elections.
Now, just like everyone else, he's in wait-and-see mode.
"I'm not certain I'm the majority leader yet — as you all may have noticed — that will be determined in Georgia," McConnell told reporters Friday in Kentucky. "So this is not yet decided in this overwhelmingly close national election."
Georgia has been a red stronghold in recent years, but the changing electorate has given Democrats hope in 2020, Gillespie said. Especially when compared to the last time the state saw a Senate runoff in 2008.
That year, Republican incumbent Sen. Saxby Chambliss beat Democrat Jim Martin by more than 300,000 votes.