It's not a popularity contest
A common misconception about the US election is that winning a majority of the votes wins the presidency. That’s not how it works. Hillary Clinton won the national popular vote for the Democrats in 2016, as did Al Gore in 2000, and neither became president.
Technically speaking, voters in the US don’t directly elect the president. Yes, you read that correctly. The US has an in-direct democracy, meaning the president is actually elected by a process called the Electoral College.
This has nothing at all to do with actual colleges or universities. It is a process by which a group of officials vote on a state-by-state basis for the US president.
The Electoral College was written into the US Constitution by the founding fathers to act as an intermediary between voters and candidates and prevent the American people electing a despot or tyrant.
The race for 270
Across the US, there are 538 total electors, with a certain number allocated to each state.
The number of electors each state has is determined by the number of people it has in Congress. Essentially, the more populous the state, the more electors it has. California has 55 electors, Texas has 38 and Florida has 29. Alaska, Montana and Idaho have only 3 each.
In every state, each political party has its own ‘slate’ of electors. On election day, US citizens are essentially voting for which slate of electors will represent their state.
If, for example, Mr Trump secures the popular vote in the state of Oklahoma, then it will be the Republican Party’s slate of electors that get to cast their votes.
It’s a winner takes all scenario where the margin of victory doesn’t matter. Even if a candidate wins a state by only one vote, they will claim all of that state’s electors to count towards their total. To use the same example, if Mr Trump wins Oklahoma, he commands all 7 of that state’s electoral votes.
The candidate that secures the magic number of 270 or more electoral votes wins the presidency.
So there's another vote?
While it does happen, electors rarely vote against the wishes of their respective states or parties. That’s how we can predict with a high degree of certainty who will win the presidency, once the official voting results begin coming in on the night of the election.
Around one month after election day, on the first Monday after the second Wednesday in December, the electors meet in each of their respective states and cast their ballots.
That’s where the direct vote actually takes place and the US President is formally elected.
US Election 2020: Battleground states explained
The key states to watch
‘Blue’ states like New York, California and Illinois have voted Democrat in each of the last four elections. ‘Red’ states like Alabama, Mississippi and Utah have voted Republican in each of the last four elections.
Then there are the purple states, usually between five to 10 states in each election that could change which party they support. These are also referred to as ‘battleground’ states and are often where the election is won or lost.
Ohio, Pennsylvania, Michigan, Florida, Wisconsin and Iowa voted for Barack Obama in 2008 and 2012 but flipped to Mr Trump in 2016.
In doing so, and despite small margins, Mr Trump earned a comfortable victory over Mrs Clinton through the Electoral College; 304 electoral votes to 224.
There could also be significant shifts in traditionally Republican states like North Carolina, Georgia, Arizona and even Texas this time around.
Is the Electoral College a good thing?
It's important to remember that winning decisively in a few states is not as meaningful as winning narrowly in several states.
Democrats poll very well in populous urban cities, but those big margins of victory don’t count for anything in the Electoral College. It’s a winner takes all system, where the winner by any margin claims all of that state’s electoral votes (except for in Maine and Nebraska, the only states that do allow split electoral votes).
This explains how Mrs Clinton won the national popular vote by three million votes in 2016 but lost the presidential race. Those extra votes basically, didn’t count for much.
There are currently calls in the US, mostly from Democrats, to reform the Electoral College system. Mr Trump went from criticising it in 2012 to praising its effectiveness in 2016. No prizes for guessing what happened in between.
US Election 2020: The contest for Congress
Why demographics matter
Both Mr Trump and Mr Biden are white men in their 70s, each leading political parties with a predominantly white membership base.
The Democrats traditionally have been the preferred political party of minority groups in the US, including African-Americans, Hispanics and Asians, and that was reflected in the 2016 election, according to exit polls analysis from the Pew Research Centre.
Mrs Clinton secured around two-thirds of the Latino vote in 2016, but it was a 10 per cent drop from that community’s support for Mr Obama in 2012. Meanwhile, Mr Trump performed well among white, non-Hispanic voters, securing 58 per cent of available votes to Mrs Clinton’s 37 per cent.
Mr Trump also secured only eight per cent of African-American votes, roughly the same as his Republican predecessor Mitt Romney did in 2012.
A majority of men voted for Mr Trump over Mrs Clinton (53 to 41 per cent), while a similar percentage of women supported Mrs Clinton over Mr Trump.
In 2016, older voters preferred Mr Trump while younger voters preferred Mrs Clinton, but support among younger voters for Mrs Clinton in 2016 was not as strong as it was for Mr Obama in 2012.
Younger people are also traditionally less likely to vote.
Republicans, in general, are more likely to vote than Democrats.
Education level and voter behaviour
Perhaps the most striking result from the 2016 election was the divide in votes based on a person's education level, with a significant gap between those with and without a college degree.
According to more analysis from the Pew Research Centre, college graduates backed Mrs Clinton by a nine-point margin (52-43 percent), while those without a college degree backed Mr Trump 52-44 per cent.
It was by far the widest gap in support among college graduates and non-college graduates in exit polls dating back to 1980.
In 2016, a majority of voters in populous, urban areas voted for Mrs Clinton (59 to 35 per cent) while a similar majority in rural areas voted for Mr Trump (62 to 34 per cent). The suburban vote was much closer, won by the Republican Party by five points (50 to 45 per cent).
What to expect on election night
Voters go to the polls on 3 November in the US.
In previous elections, voting results begin coming in by the evening (US time) on election day, and a winner is declared later that night. Last year, Mr Trump declared victory at around 3am the day after.
This year is almost certain to be different. Due to COVID-19, there will be a much higher number of early and postal votes that will need to be counted. Depending on how close the votes are, it could take days, weeks or even months.
As responses to COVID-19 in the US have become so politicised, it is expected that more Democrat voters will make use of early and postal voting, while Republican supporters are more likely to show up at a polling booth on the big day.
That means the early polling numbers that come in on election night, will likely show support for Mr Trump, but the early and postal votes to be counted later will likely deliver a surge for Mr Biden.
A narrow margin of support for Mr Trump before early and postal votes are counted probably won’t be good for the Republicans.
Can you trust the polls?
Mr Trump was elected on an anti-establishment platform that promised to push back against globalisation and grow jobs in middle America. Polling indicates that he is still the more trusted candidate when it comes to the economy.
In 2020, his promise to ‘Make America Great Again’ goes beyond the economic. In the face of nationwide Black Lives Matter protests, he has branded himself a champion of law and order.
Conversely, Mr Biden will be hoping not to repeat the mistakes of his predecessor. Mrs Clinton largely assumed victory in battleground states where the polls showed her leading. The polls, as we now know, were wrong.
If Republican voters in traditionally red states do not abandon Mr Trump in 2020, it will again be voters in key battleground states that decide the election.
Whoever wins, there will be an inauguration ceremony at the White House on 20 January, which officially marks the start of the president’s four-year term.