By Jason Lange and Brad Heath
(Reuters) - The future of Democrat President-elect Joe Biden's agenda hinges on two Senate runoff races in Georgia whose outcome might not be known for days after polls close on Tuesday.
Public opinion polls show Republican incumbents Kelly Loeffler and David Perdue have about the same level of support as their Democratic challengers Raphael Warnock and Jon Ossoff.
Following are key facts on the vote-counting process and what to expect as election returns start to come in Tuesday night.
WHY MIGHT THIS DRAG ON?
Slow counting of Georgia's mail ballots in November's presidential election kept the world in the dark about who won the state until three days after polls closed. Biden ended up winning the state by less than 12,000 votes out of about 5 million cast.
A similar delay could unfold after Tuesday's contests if the races are really close, said Walter Jones, a spokesman for the office of Georgia's top election official, Secretary of State Brad Raffensperger.
"We may be looking at several days," Jones said, adding that the delay would mostly come from mail ballots returned on Election Day.
Election officials cannot start counting ballots until 7 p.m. on Tuesday, though they have started processing them, such as checking that voter signatures on mail ballots match those on record.
Nearly 1 million mail-in ballots have been processed through Sunday, state data shows. These ballots, as well as more than 2 million cast in person at early voting centers, will likely be counted quickly on Election Night.
But for the mail votes that arrive on Election Day, officials will still need to open envelopes, check signatures and load the ballots in counting machines. They will also need to process hundreds of thousands of votes expected to be cast in person that day.
In November, mail ballots heavily favored Biden in Georgia and other swing states, while President Donald Trump led in votes cast in person. If more Democrats again vote by mail this time, initial results could similarly show Republicans in a lead that gives way to Democrats catching up.
The slow counting of mail ballots was a key reason why Trump took an early lead on Election Night on Nov. 3, only to trail Biden in the days that followed as more mail ballots were counted.
In the end, about a quarter of Georgia's ballots in November were cast by mail and Biden won about two-thirds of them, state data shows. The rest were cast in person, with about 55% going to Trump.
"Initial results will generally reflect the state of the race but probably will be a little redder than what they will end up being," said Kyle Kondik, a political analyst at the University of Virginia's Center for Politics.
Georgia did two recounts of November's presidential contest: a hand recount of paper ballots ordered by the state's top election official, and a subsequent recount using computer scanners that was requested by the Trump campaign.
Georgia allows a losing candidate to force a recount if the margin of victory is less than or equal to 0.5% of the total vote in the race. A recount must be requested within two days of the results being certified by election officials.
Candidates can also request a recount if they think there has been an error in the tabulation; in that case it's up to the secretary of state to decide whether to conduct one. Local election officials also have the power to recount results in their county before the results are certified.
(Reporting by Jason Lange and Brad Heath; Editing by Soyoung Kim and Dan Grebler)