What is a primary? US 2020 election terms defined

It’s the main way candidates for the two major parties are chosen for the US presidential election. But what exactly is a primary?

For a long time it was anyone's guess who Donald Trump's opponent would be in this year's election.

It could have been Bernie Sanders, Pete Buttigieg, Elizabeth Warren, Michael Bloomberg or any of a dozen or so others who threw their hat in the ring. So how did it come to be Joe Biden? The answer is his success in the Democrat party's primary elections.

Primary elections are the main way candidates for the major parties - Republican and Democrat - are chosen for a US presidential election.

A public vote is held for each party, in each state, starting in February of the election year. When voters cast their votes in these primary elections, what they're really doing is voting for delegates to pledge their support for the state's choice of candidate to be confirmed at the party's convention in August.

“Primary Season”, as it is sometimes known, usually starts with a large number of candidates vying for the nomination, with the number of candidates decreasing as time goes on, as some candidates drop out when it becomes clear they have no chance of winning.

Once each party's candidate is confirmed at the Republican or Democrat convention, campaigning then begins in earnest ahead of the presidential election held in November.

Democratic presidential hopefuls Pete Buttigieg, Elizabeth Warren and Joe Biden participate in the fifth Democratic primary debate of the 2020 presidential campaign. Picture: Saul Loeb / AFP

DO YOU HAVE TO BE A MEMBER OF A PARTY TO VOTE IN A PRIMARY?

The rules of primary elections vary from state to state. There are two types of primaries: closed and open. At closed primaries, people can only vote in their party's primary election if they are registered members of the party before election day. Closed primaries are held in 13 states including Connecticut, Florida, Wyoming and Maryland.

At open primaries, voters don't have to be party members and can vote in either party's primary but not both. So while you'd assume a Democrat would vote to elect their own party's candidate, that person could instead choose to strategically vote for a Republican candidate in a bid to eliminate an opposition frontrunner from the competition. States with open primaries include Alabama, Missouri and Virginia.

DOES EVERY STATE HAVE A PRIMARY?

No. States choose one of two methods for selecting party candidates. States that do not have primary elections instead use caucuses. Caucuses are meetings where party members gather to debate, listen to candidates or supporters and then vote publicly one way or another. This can be a longer and more drawn-out process than an election, which simply involves a voter marking a ballot paper.

DOES A SITTING PRESIDENT HAVE TO GO THROUGH THE PRIMARIES?

If a first-term president is seeking re-election for their party, like Donald Trump is this year, they'll usually receive the nomination of their party without any opposition. Sometimes primary elections are still held, but they are a formality. At other times they are cancelled in order to show unity behind a candidate and redirect the money that would have been spent on the expensive election process to the candidate's re-election campaign.

DID DONALD TRUMP FACE ANY OPPOSITION WITHIN THE REPUBLICAN PARTY THIS YEAR?

In April 2019, former Massachusetts governor Bill Weld announced his candidacy as a long-shot challenger to Mr Trump in the Republican Party. Other candidates also emerged including former congressman Joe Walsh and former South Carolina governor Mark Sanford. None of these candidates enjoyed success and Mr Trump became the presumptive nominee for the Republican party in March 2020.