Any prospective presidential candidate must meet three criteria. They must be a US citizen from birth; at least 35 years old; and have lived in the US for at least 14 years.
The two main political parties hold primaries and caucuses across the country during an election year to select who they want to represent them on the ballot. You can read more about that process here.
The Democratic and Republican candidates are then formally selected and announced during their parties’ summer conventions. At this stage in the campaign, it is already clear that Mr Biden, the former US vice president, will be the Democratic nominee to take on Mr Trump.
The US election system itself is far from straightforward. That is because when America’s founding fathers created the system in 1787, there was no way a presidential candidate could mount a national campaign – and there was little in the way of national identity.
The founding fathers chose not to elect US presidents by direct popular vote over fears that larger and more populous states could have an outsized role in deciding the winner.
The system of electors, based loosely on the Roman Catholic College of Cardinals selecting the Pope, was chosen with the theory that the most knowledgeable and informed individuals from each state would select a president on merit, disregarding state loyalties.
So when Americans cast their vote on November 3, they technically vote for “electors”, not the candidates themselves. The electors are state officials or senior party figures, but they are not usually named on the ballot.
Each elector casts one vote following the general election for one of the two candidates. The newly elected President and Vice President will then be inaugurated on January 20, 2021.
How does the electoral college work?
All 50 US states and Washington DC have a set number of “electors” in the electoral college – roughly proportionate to the size of each state.
Each state gets at least three electoral votes because the amount is equal to its total number of Senators and Representatives in the US Congress. Washington DC also gets three electoral college votes, meaning a total of 538 electors form the Electoral College.
California, the largest state, has 55 electoral votes, Texas, the next largest, gets 38. New York and Florida have 29 each.
All but two states – Maine and Nebraska – use a winner-takes-all system, so if you win the most votes in a state, you take its entire haul of electoral college votes.
To become president either candidate needs to win a majority of the 538 electors – i.e. 270 electors.
While the Constitution does not dictate that electors follow the popular vote, many US states have laws requiring them to do so. These laws have been challenged by electors voting for someone else on occasion, but in July, the US Supreme Court ruled that electors must follow the popular vote in states that have passed such a law.
The electoral college system does usually reflect the popular vote – presidents have won the electoral vote while losing the popular vote just five times in US history. The most recent instance was in 2016, when Donald Trump won the electoral college but Hillary Clinton, his Democratic opponent, won the popular vote.
What are swing states?
The key for either party to win the presidential election is to target specific battleground states. There are several swing states, that over recent elections have gone both ways. They hold the key to winning the election.