Officials across the country are warning Americans of the possibility that the full results of Tuesday's midterm elections might not be known for days.

And what's more, we may not know the balance of power in Congress for weeks, or even a month.

Looking back at the 2020 presidential election, which was held on Nov. 3, 2020, it took until Saturday, Nov. 7, for The Associated Press and other news outlets to project that Joe Biden defeated incumbent President Donald Trump.

And thanks to no candidate in either of Georgia's U.S. Senate races claiming an outright majority of the vote in November's contest, the makeup of the Senate – and control of Congress – was not determined until Jan. 5, 2021, weeks before Biden's inauguration.

While it's possible that the wait might not be that long this year, it's possible that we may not know all of the results on election night. As such, officials are warning Americans to prepare for possible delays – and get ahead of potential false claims of a rigged election.

In a speech last week in Washington about threats to democracy, President Biden took time to celebrate strong early voting numbers, while acknowledging the results might not be known right away.

"We’re seeing record turnout all over the country, and that's good," Biden said. "We want Americans to vote. We want every American’s voice to be heard. Now we have to move the process forward."

"We know that more and more ballots are cast in early voting or by mail in America, and we know that many states don’t start counting those ballots until after the polls close on Nov. 8," he added. "That means, in some cases, we won’t know the winner of the election for a few days — until after a few days after the election. It takes time to count all legitimate ballots in a legal and orderly manner."

"It’s always been important for citizens in a democracy to be informed and engaged," Biden said, before acknowledging Tuesday's election will be the first since the Jan. 6, 2021, riot at the U.S. Capitol. "Now it’s important for citizens to be patient as well. That’s how this is supposed to work."

Biden's comments have been echoed by a number of state officials, as well as the Cybersecurity and Infrastructure Security Agency, which published a roundup debunking false election rumors.

"The timeline for reporting election results may be impacted by a number of factors, including changes to state or local level policies that affect how the election is administered, changes to when ballots can be processed, or additional protocols implemented to make voting and vote processing safer during the pandemic," the agency wrote. 

"Election results reported on election night are always unofficial and are provided solely for voters’ convenience," CISA's bulletin read. "In fact, no state requires that official results be certified on election night itself. Fluctuations in unofficial results reporting will occur during and after election night as more ballots are processed and counted, often including military and overseas ballots and validated provisional ballots."

In 2020, President Donald Trump proclaimed that the lack of final results on election night could be an indicator of something nefarious, using it to falsely assert that the election was stolen: "We don’t want them to find any more ballots at 4 o’clock in the morning and add them to the list."

There was no evidence of any widespread voter fraud in the 2020 presidential election, a claim backed up by officials in Trump's own administration, including attorney general William Barr. Cases alleging fraud brought by Trump and his allies were rejected from courts nationwide, all the way up to the U.S. Supreme Court.

On Monday morning, the campaign of Pennsylvania U.S. Senate candidate John Fetterman sent out a memo warning voters to "buckle up for a long week."

"We should all be prepared for a process that takes several days before all eligible votes are properly counted and the results are clear," wrote Fetterman campaign manager Brendan McPhillips. 

"The reality is Pennsylvania law means in-person votes that skew Republican tend to disproportionately be counted and reported before Democratic-leaning mail-in votes," McPhillips wrote, adding: "Similar to 2020, the reality is it will take time – likely several days – to count the votes accurately and ensure every eligible vote is counted."

Here's what you need to know:

In reality, results released on election night are unofficial and always incomplete. They inevitably change as more ballots are counted.

Unlike in many countries, elections in the U.S. are highly decentralized, complex and feature long lists of races, from president and Congress all the way down to local measures and town council seats. Some states give local election offices several weeks before Election Day to process mailed ballots, including checking signatures and verifying ID information. In other states, that process can't start until Election Day or shortly before, meaning those ballots might not get counted until the next day or even later.

Republicans in particular have pointed to perceived delays in knowing results as a reason to be suspicious about the integrity of elections.

“We’ve got to get our elections reformed so that every Arizonan, whether they be Democrat, Independent, or Republican, when they go to bed on Election Night they know the winner and they’re satisfied that it was a fair election. We don’t have that right now,” Kari Lake, the Trump-endorsed Republican candidate for governor in Arizona, said in August on Twitter.

Not knowing the winner on election night says nothing about the fairness of an election or the accuracy of results. Under Arizona law, all ballots including those that were mailed must be returned by 7 p.m. on Election Day, but officials have 20 days to finalize their counts.

In Nevada, counties have four days to count late-arriving mailed ballots and give voters two more days to fix mailed ballots that arrive in envelopes with errors or missing information. This week, the elections official in the county that includes Reno reminded voters of that extended timeline and said final, official results are unlikely until the actual canvass of the vote on Nov. 18.

“It will definitely be more than the day after the election for final results of the election," said Jamie Rodriguez, Washoe County's interim registrar of voters.

A close Republican primary for U.S. Senate in Pennsylvania last May triggered comparisons to the French presidential election, which had been held a few weeks earlier.

Trump, in a social media post two days after the Pennsylvania primary, questioned why it was taking so long to find out the winner: “France, same day all paper, had VERIFIED numbers in evening,” Trump wrote. “U.S. is a laughing stock on Elections.”

But in France there was only one contest on the ballot. Presidential and parliamentary elections are held on separate dates. In Pennsylvania, the U.S. Senate GOP primary was just one of several contests being decided, including races for governor, attorney general, Congress and state legislature.

U.S. elections also are not nationalized, but rather overseen by states and run by local officials at the county or even township level. The U.S. has some 10,000 jurisdictions charged with overseeing the voting process.

For presidential elections in France, the Ministry of Interior distributes election-related materials, including ballots, while local officials coordinate staffing of polling places. France also has a Constitutional Council that decides election-related complaints and announces results.

Noah Praetz, the former elections clerk in Cook County, Illinois, said it’s possible to have quick results, but the U.S. has “decided to make voting accessible to everybody and let us vote on everything.” He noted that ballots in the U.S. typically include dozens of offices in contrast to some countries where voters might simply back a party whose leadership then fills many of those positions.

In France, voters choose from lists of local candidates usually associated with a party. The candidate list gaining the most support will receive the most seats in the city and regional councils.

“It’s a fundamentally different view of democracy,” Praetz said.

In addition, voters in France can vote by proxy — designating someone else to vote for them if they are unable to cast a ballot in person on Election Day, which is not allowed in the U.S.

They can. Long before the COVID-19 pandemic, states were expanding the use of mail ballots and early in-person voting to reduce lines on Election Day and provide more flexibility to voters.

Mail ballots are subject to various security checks, varying by state. Some require voter signatures or ID information to match their registration files, while others require witnesses or notaries to affirm a voter’s identity.

In most states, including Florida and Georgia, the process of validating mail ballots begins well ahead of Election Day -- providing a huge advantage in reporting results quickly. That's not the case in a few political battleground states. Pennsylvania and Wisconsin officials are not allowed to begin that work until Election Day, while Michigan officials can start just two days before. This means most results being reported from these states on election night will be from in-person voting on Election Day or during the early voting period.

“Counting votes and reporting the results take time,” said Leigh Chapman, acting secretary of state in Pennsylvania. “Election officials are focused on accuracy over speed.”

While most states require mail ballots to be received on or before Election Day, 19 states provide a grace period as long as ballots were sent through the mail by Election Day. Such ballots in California can be received up to seven days later.

Voters may not know the outcome of a close race for several days if a significant number of those ballots arrive at local election offices after Election Day.

This also can change results over time. If Democratic voters dominate mail voting while Republican voters largely cast ballots in person, this can mean that early results heavily favor a Republican candidate who then sees that lead slip away as the late-arriving mail ballots are counted.

No. Hand counting of all ballots happens primarily in small towns in the Northeast. For places with a lot of ballots, experts consider it to be more time-consuming and susceptible to human error. Hand tallies are used in post-election reviews to ensure accuracy of tabulator machines, but that usually involves only a sample of ballots and is done without the time pressure of trying to report results quickly.

Republican activists and candidates have been pushing for hand counts, based largely on conspiracy theories that voting systems were manipulated to steal the 2020 election. There is no evidence of widespread fraud or tampering of machines.

Also, hand counts would by themselves prolong the reporting of results, perhaps by several days.

Cobb County, Georgia, performed a hand tally ordered by the state after the 2020 election. It took hundreds of people five days to count just the votes for president on roughly 397,000 ballots. A county election official estimated it would have taken 100 days to count every race on each ballot using the same procedures.