ATLANTA (NEXSTAR) — With control of the U.S. Senate at stake, all eyes are on a runoff election that has Republicans David Perdue and Kelly Loeffler facing Democrats Jon Ossoff and Raphael Warnock. Millions of dollars have poured in, Georgians have been bombarded by advertisements and messages urging them to vote, and both sides have sent their heavy hitters to help turn out voters.

Some things to keep in mind as the polls close Tuesday night:

HOW DID WE GET HERE?

Perdue got about 88,000 more votes than Ossoff in the general election, but a Libertarian candidate’s 115,000 votes kept him from topping 50%, which is required to win. Gov. Brian Kemp appointed Loeffler to the Senate in December 2019 after Sen. Johnny Isakson stepped down. She and Warnock were competing in a 20-candidate special election to serve the two years remaining in Isakson’s term. Warnock got 1.6 million votes, while Loeffler got nearly 1.3 million and Republican U.S. Rep. Doug Collins placed third with nearly a million votes.

WHEN DOES THE BALLOT COUNTING START?

The polls are set to close at 7 p.m. EST on Election Day, and that’s when ballot counting can begin. Absentee ballots must be received by the close of polls to be counted. Military and overseas ballots postmarked by Tuesday and received by Friday will be counted, and absentee voters also have until Friday to fix any problems so their votes can be counted.

No ballots, including absentee ballots received in advance of Election Day, can be counted until the polls close. But a state election board rule requires county election officials to begin processing absentee ballots — verifying signatures on the outer envelope, opening the envelopes,and scanning the ballots — before Election Day. That should speed things up on election night. Still, some absentee ballots received by mail or in drop boxes up until 7 p.m. on Election Day will still need to be processed.

WILL WE KNOW THE WINNER ON ELECTION NIGHT?

Just like in November, it’s very possible Americans will go to bed without knowing who won. All indicators point to the likelihood of very tight margins in both races.

Media organizations, including The Associated Press, often declare winners on election night based on the results that are in, voter surveys and other political data.

But in a close race, more of the vote may need to be counted before the AP can call a winner.

THE LEAD MAY VERY WELL SHIFT AS VOTES ARE COUNTED

In a close contest, look for the Republican candidate to jump out to an early lead. That due to two factors: First, Republican areas of the state usually report their results first. Second, Republican voters have been more likely to vote in person, either on Election Day or during the early voting period. Many counties release those in-person results first.

Meanwhile, heavily Democratic counties, including Fulton, DeKalb and Chatham counties, historically take longer to count votes. Democratic candidates could also make late surges because of late-counted mail ballots, which heavily favored Ossoff and Warnock, as well as Joe Biden, in November.

In November, Perdue held a lead of about 380,000 votes over Ossoff at 10 p.m. EST on election night. But Perdue’s lead eventually fell below 90,000.

In a very tight race, it could take several days to determine a winner. In November, more than 5 percent of Georgia’s votes were counted after noon on the day after Election Day. At that time, Donald Trump led Biden by 100,000 votes in a race that Biden eventually won after all the mail ballots were counted.

GEORGIA’S DONE A LOT OF BALLOT COUNTING ALREADY THIS ELECTION CYCLE

That is true and the trend could continue with the runoff. Under Georgia law, if the margin separating the candidates is within 0.5%, the losing candidate has the right to ask for a recount. That would be done by running the ballots through the scanners again, as happened when President Donald Trump requested a recount after the results showed him losing to Biden by about 12,000 votes.

But we’re not likely to see a full hand recount like the one done for the presidential race during the general election. That was triggered by a requirement that one race be audited by hand. Secretary of State Brad Raffensperger chose to audit the presidential race and said the close margin in that contest required a full recount. Deputy Secretary of State Jordan Fuchs said the audit requirement doesn’t apply to runoff elections.

FINAL WARNINGS ABOUT HIGH-STAKES RUNOFFS

Democrats and Republicans alike are casting Tuesday’s twin Georgia Senate runoffs in the starkest of terms as the state prepares for last-minute visits from President Donald Trump and President-elect Joe Biden before elections to decide which party will control the Senate at the outset of Biden’s tenure.

Perdue, who is fighting for a second term against Democratic challenger Jon Ossoff, said Monday “the very future of our republic is on the line” as he addressed by telephone a megachurch crowd gathered to see Vice President Mike Pence.

Declaring the duty to vote “a calling from God,” Perdue said the outcome in Georgia “will determine the future of our country for maybe 50 to 100 years.”

Those watching from afar were no less dramatic.

“The people of Georgia have an opportunity to change the course of the nation’s history at this moment,” said Rep. Hakeem Jeffries, a New Yorker who chairs the House Democratic Caucus.

Republicans need just one more seat to maintain Senate control and force Biden to contend with divided government. Democrats need a sweep for a 50-50 split that would make Vice President-elect Kamala Harris, as the Senate’s presiding officer, the tiebreaking vote.

The stakes have drawn a flood of campaign spending measured in the hundreds of millions of dollars, with Trump and Biden making multiple trips to the state that finds itself newly atop the nation’s list of battlegrounds. Biden won Georgia’s 16 electoral votes by about 12,000 votes out of 5 million cast in November, though Trump continues to push false assertions of widespread fraud that even his attorney general and Georgia’s Republican secretary of state — along with a litany of state and federal judges — have said did not happen.

The president’s trip Monday comes a day after disclosure of a telephone call he made to the Georgia secretary of state over the weekend to pressure Republican Brad Raffensperger to “find” enough votes to overturn Georgia’s election results ahead of Wednesday’s joint session of Congress to certify Biden’s Electoral College victory. The call highlighted how Trump has used the Georgia campaign to make clear his continued hold on Republican politics.

Trump is scheduled for a nighttime rally in north Georgia. Biden will campaign in Atlanta in the late afternoon with Ossoff and Warnock.

Perdue, whose first Senate term expired Sunday, and Sen. Kelly Loeffler, an appointed senator trying to win her first election, have spent the two-month runoff blitz warning that a Democratic Senate would herald “radical” and “dangerous” lurch to the left.

Democratic challengers Ossoff and Raphael Warnock have blasted Republicans as obstructionists, pointing to how Senate Majority Leader Mitch McConnell stymied President Barack Obama, and insisted that recovering from the nation’s ability to confront the coronavirus pandemic hinges on a Democratic majority.

To be sure, a closely divided Senate — with the rules still requiring 60 votes to advance major bills — makes the prospects of sweeping legislation difficult regardless. But a Democratic Senate would at least assure Biden an easier path for top appointees, including judges, and legitimate consideration of his legislative agenda. A Senate led by Republicans and McConnell would almost certainly deny even an up-or-down vote on Biden’s most ambitious plans on health care, taxation and the environment.

More than 3 million Georgians already have voted. The last-minute push is focused on getting voters to the polls Tuesday. Democrats ran up a wide margin among 3.6 million early votes in the fall, but Republicans countered with an Election Day surge, especially in small towns and rural areas.

Even with Biden’s statewide win, Perdue led Ossoff by 88,000 votes, giving the GOP confidence in the runoff. The runoffs were required because none of the candidates reached a majority vote, as required by Georgia law. Despite Perdue’s initial advantage, early voting figures suggest Democrats have had a stronger turnout heading into Tuesday, and leading Republicans have expressed concerns about the pressure that puts on their turnout operation.

Monday’s itinerary shows how the two sides plan to hit their targeted voters.

Biden will be in the core of metro Atlanta with Ossoff and Warnock, where Democrats have capitalized on rapid population growth and suburban shifts away from Republicans. Trump will be in the north Georgia town of Dalton, the population center of one of the state’s most Republican congressional districts where the president’s appeal among small town and rural Georgians helps offset Democrats’ more city-based coalition.

In states less diverse and less urbanized than Georgia, Trump’s reach was enough to propel several vulnerable GOP senators to comfortable victory margins, setting up the Georgia runoffs to tip the scales in the Senate.

Pence, meanwhile, was in Lamar County on the outskirts of the sprawling metro Atlanta footprint — an exurban enclave that could be the tipping point between the two parties’ respective strongholds.