Many millions of eyes around the world could find themselves glued to data emerging from Pennsylvania sometime around midnight eastern time on U.S. election night.

It comes down to the math of presidential elections — and how the pandemic has permanently altered it by popularizing mail-in voting, especially among Democrats.

Nowadays, predicting the winner requires factoring in results from both mail-in and in-person ballots, along with how many of each remain uncounted.

It so happens that Pennsylvania, the state that's probably most critical to crowning the winner, has a law requiring the vast majority of its counties to publish some mail-ballot statistics by 12:01 a.m. ET on Wednesday, Nov. 6.

News organizations' number crunchers will then plug those stats into spreadsheets and calculate the likelihood of either candidate emerging victorious in that vital state.

By that point, we should already have a sense of who the frontrunner is, courtesy of two southeastern swing states: Georgia and North Carolina. 

The polls close in Georgia at 7 p.m. ET and in North Carolina at 7:30 p.m. ET, and both states have laws that should enable timely processing of mail ballots. 

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A top election-data analyst expects to have a good idea who's won those southern states sometime between 10 p.m. and 11:30 p.m., unless it's too close to call. 

"That's going to be our first set of clues to how this may go," said Drew McCoy, president of the election-reporting service Decision Desk HQ.

In summary: If either candidate wins both southern swing states, they immediately become the commanding favourite. In the case of Donald Trump, he would be on the cusp of victory. If he subsequently wins Pennsylvania, it's lights out: the 45th president is a near-lock to become the 47th president.

Pennsylvania's potentially decisive data dump

"It's over," if Trump wins North Carolina, Georgia and Pennsylvania, McCoy said. He would hit the magic number of 270 electoral votes, barring a shock event like Harris winning, say, Texas or Florida.

In other words, Pennsylvania becomes the kingmaker. Which brings us to that midnight data dump.

Under a law passed in 2022, Act 88, the state's 67 counties were offered grant money for new election equipment and staff, but there are strings attached: To get the cash, they have to publish data on the number of outstanding mail ballots.

The mail ballots take longer to process. It requires opening envelopes, checking signatures, confirming the identity of voters, placing ballots in piles, then sliding them into machines.

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This delays the counting of ballots that tend to skew Democratic, which distorts the early reporting on the election result.

Now all Pennsylvania counties except two tiny ones have agreed to the cash conditions. They must publish the number of mail ballots still uncounted on county websites, no later than 12:01 a.m.

By then, the entire election-watching world can grab the data from a cross-section of counties, from cities, to suburbs, to rural areas; estimate the number of remaining mailed votes per party based on the breakdown so far; and calculate the likely winner.

Results will emerge more slowly in other states.

Some swing states will be slower

In Wisconsin, Milwaukee officials have warned not to expect mail-in ballot results before midnight, as the entire county has 13 machines and is forbidden by law from starting to process these ballots before the morning of election day. McCoy doesn't expect a clear portrait from Milwaukee until the wee hours — sometime after midnight, probably closer to 4 a.m.

In Michigan, new laws allow earlier handling of mail-in ballots. But the top election official isn't promising results until the next day. On Face The Nation, Jocelyn Benson said she hopes it's sooner, but added: "I would estimate end of the day on Wednesday."

Arizona and Nevada, like many western states, have a long history with voting by mail. But a detail in their laws could delay the result. Both states count mail-in ballots even if they arrive after election day.

In Arizona, they can arrive up to 10 days later. Those late arrivals typically involve a tiny percentage of ballots, but if it's a close result, it still complicates declaring a winner. A blowout would make a quicker call possible.

Here's a nightmare scenario for Nevada's secretary of state: That the election comes down to the six electoral votes in his state, which suffers delays in the counting.

"That is my biggest fear that keeps me up in the middle of the night," Cisco Aguilar said during an online panel earlier this year. That's why Nevada implemented reforms aimed at speeding up counting, increasing the chances of a same-day projection.

After the days-long counting drama in 2020, other states also have new laws to speed things up. Like the western states, Michigan and Georgia now allow mail ballots to be opened before election day, so the count goes faster that day. 

But similar reforms failed in Wisconsin and Pennsylvania. Those two states have one thing in common: Their Republican-controlled legislatures blocked bills that would allow earlier processing.

Some members of the Pennsylvania legislature expressed frustration in interviews, describing how the House, run by Democrats, passed different pre-processing bills that were left to die in the Republican-controlled Senate.

A top Pennsylvania Democrat said parliamentary rules forbid him from questioning the motives of his adversaries on the legislature floor.

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2020 delays abetted a democracy-straining debacle

But, in his mind, it's no mystery why Republicans have blocked faster ballot-counts: Because Donald Trump doesn't want it. Later counting of mailed votes, if they skew Democratic, helps him prematurely declare victory, as he did in 2020.

"It's the worst possible reason," said the Democrats' state House majority leader, Matt Bradford, over a coffee in his area outside Philadelphia.

"It's pretty clear what this is about. They're doing the bidding of Donald Trump. They are worried that he will come out against them and say horrible things." 

Pennsylvania's legislature did pass, with bipartisan votes, the above-mentioned compromise bill that requires the pre-12:01 a.m. publishing of the total number of outstanding mail-in ballots. Which, again, could help project a winner. 

The state's top election official has his own concerns. Al Schmidt, the secretary of state, says these delays are a stress-test for American democracy. In 2020, a multi-day information vacuum became a petri dish for conspiracy theories. 

Amid the slow count, protests began, triggering weeks of unrest that culminated in the attack on the U.S. Capitol on Jan. 6, 2021. 

Schmidt, a Republican, recently told 60 Minutes that those delays are when people start making wild claims "about truckloads of ballots. And that's when you start hearing about zombie voters and that's when all this other stuff really starts pouring in."

"The message is: Please be patient."

That said, he's hopeful things will go more smoothly this time, as officials have newer equipment, better training and more experience with mail-in ballots.

It's a point stressed by Decision Desk HQ's McCoy, too. He's optimistic this year will be easier.

After all, four years ago, multiple states were, like Pennsylvania, deploying mail-in ballots for the first time on a massive scale, in a hurry, amid a wave of public-health precautions. They not only have more experience now, but also fewer mail-in ballots to process compared to the pandemic election four years ago. He describes the last election as a perfect storm.

"I think 2020 was so unique simply because of COVID. You know, we've had close elections in this country before — 2000 comes to mind. But the confluence of events around … holding a national election in the pandemic, I think, will always set that apart," McCoy said. 

"Hopefully, we won't ever experience anything like that again."