Jon Henley explains:
What usually happens?
US presidential elections are not won by the national popular vote. The winner in each state collects its electoral college votes – and needs a total of 270 to take the White House.
In most elections the result is clear – although not officially confirmed – by the end of the night. Major American media outlets “call” each state for one of the candidates. While not based on the final vote count, that projection is almost invariably accurate.
This means an accurate tally of electoral college votes can be made and a winner declared. In 2016, that happened at 2.30am in Washington when Trump reached the required 270.
Why is that not happening this time?
Mainly because of the Covid-19 pandemic, large numbers of voters – about 68% of the total, compared with 34% in 2016 – cast their ballots early, including by post.
Counting postal votes is slower because voter and witness signatures and addresses must be checked, and ballots smoothed out before being fed into counting machines. Some states start that verification process long before election day, meaning the count itself can get under way as soon as polls close. Others, however, do not allow that.
Which states are we talking about?
Five states have yet to be called: Nevada, Georgia, North Carolina, Pennsylvania and Alaska. Several news organizations, including the Associated Press and Fox News’ decision desk, have called Arizona for Joe Biden. The Trump campaign is arguing, however, that call was made too early. Its next update is not due until 9pm ET on Thursday.
Alaska will end up in the Republican column with near certainty.
Pennsylvania officials say they expect most votes will be counted by Friday.
The Democratic challenger is narrowly ahead in Nevada, with only Democratic-leaning late postal ballots left to tally. Officials have said no more results will be released in Nevada until midday ET on Thursday.
In North Carolina, while Trump is the clear favourite, the state accepts postal ballots until 12 November – although that is expected to make little difference.
What else is complicating matters?
Roughly half of all states will accept postal votes that arrive after election day as long as they carry a postmark of no later than 3 November, so postal delays may mean some ballots are not processed until days later: Pennsylvania has said results will not be considered complete until the deadline of Friday.
There has also reportedly been an increase in the number of provisional ballots cast by people who asked for a postal vote but then decided to go to the polling station in person instead. These need careful checking to make sure no one has voted twice.