Even after three days of polls being closed in the US, the Americans and the world still do not have their president, although Democrat Joe Biden was on the brink of unseating Donald Trump, reported AFP.

The delay has fueled tension across the polarised nation, with the US President accusing Democrats of “engineering fraud and stealing the elections”. But the delay was widely expected, often for reasons specific to individual states, which under the US system each conduct their own polls.

California, which is the most populous state in the US, was quickly called for Biden after polls closed on Tuesday. But these calls are in fact projections by news outlets rather than official results, meaning that it takes longer to get an accurate picture in narrowly divided states.

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“The closer the races, the longer it takes,” Kathy Boockvar, secretary of the vital state of Pennsylvania, explained to reporters.

Every state has different deadlines on receiving absentee ballots, especially those coming from the military or other citizens living overseas.

For instance, North Carolina has held off on counting at least 171,000 ballots, as by law it accepts votes that arrive by mail through November 12 so long as they were postmarked by Election Day.

In Nevada, which also has a tight race, ballots will be counted postmarked by Election Day so long as they arrive by November 10. Another cause of delays are provisional ballots that are issued if there is confusion about their registration and need verification.

With concerns about the COVID-19 pandemic, states accustomed to limited numbers of absentee votes have been deluged with ballots mailed by citizens who do not want to risk voting in person.

Some 65.2 million of the record 160 million Americans, who voted this year did so by mail, according to an estimate of the US Elections Project. In Pennsylvania, the Republican-led legislature rejected an effort to let authorities count ahead of Election Day, contributing to the scenario in which its biggest city Philadelphia — a Democratic stronghold — reported returns last.

Some places have unique factors delaying vote-counting such as Chatham County in tightly fought Georgia, where an election division and a registration board separately look at ballots.

The Trump campaign has seized on the delay to demand a halt to counting in states where it is behind, notably Pennsylvania whose Republican Party approached the US Supreme Court.

Republicans had been fighting for months against allowing Pennsylvania to count ballots postmarked by Election Day if they arrive by Friday.

In Wisconsin, where Biden eked out a narrow victory in results made known by early Wednesday, the Supreme Court ruled that only votes received by Election Day would count.

Most states allow rival parties to observe counting but challenges on the rules have taken time, with Trump’s supporters taking particular issue with Philadelphia’s rule that watchers stay at least 15 feet (4.5 meters) away due to COVID risks.