Twenty years ago Americans woke up on an autumn morning after Election Day and did not know who would next lead the country. It took 36 more days to resolve the contest between Al Gore and George W Bush as the country held its breath. That prospect could happen again in 2020. Why? Well, the pandemic has many people fearful of voting in person because in the US that often means waiting for hours in a queue. So millions more will vote by post and there are fears it could take days or weeks to count them all, leaving the outcome on a knife-edge. What usually happens on a normal election night? Different states stop voting at different times. The first polls to close are on the East Coast, at about 19:00 local time (00:00 GMT), and after that you start getting a running total as votes in those states are counted. Presidents are not picked by winning a national vote. No, instead it's a series of state-wide races with the winner in each state taking a certain number of what's called electoral college votes. A state is "called" for a candidate when a media outlet believes one candidate has an insurmountable lead. It is a projection not a final result. Similarly, when the whole election is "called" for a candidate, it is not the official result because there are still lots of votes to count. An election is usually called on the night. And what follows is a choreographed response including a concession speech from the losing candidate. Perhaps not this year - more on that later. In 2016 the election was called for Donald Trump at about 02:30 EST (07:30 GMT) after winning Wisconsin put him over the 270 threshold of electoral college votes. In the days and weeks that followed, more and more Democratic votes were counted which meant Hillary Clinton stretched her lead in the nationwide popular vote but the electoral college was already lost.