View our collection of 21 interesting US election-related facts. Did you know? 1. Each US state has a process for selecting the presidential candidates for the main political parties. Some hold a secret ballot called a primary; others hold caucuses, where attendees select a candidate through open voting. 2. In some states you don't have to be a member of any political party, and can even be a member of a rival one, to vote in the primary to select a presidential candidate. 3. The Democratic Party uses a proportional method for awarding delegates – each candidate is awarded a percentage of delegates based on the results of the caucus or primary. The Republican Party allows each state to decide whether to use the winner-takes-all method or the proportional method. 4. In modern elections, each presidential candidate chooses their own vice president from their own party. Originally, however, whoever came in second in the November election was named vice president, even if they were from a rival party. 5. US national elections are always held on the Tuesday following the first Monday in November, although in some states votes can be cast as early as 45 days in advance. Early voting is either done by mail, in person at an election official’s office, or at a satellite voting location, such as a town hall, library or even a grocery store. 6. Three states, Oregon, Washington and Colorado, conduct all elections by mail. A ballot is automatically mailed to every registered voter in advance, and traditional in-person voting is not widely available. 7. North Dakota is the only state without voter registration. Despite being one of the first states to adopt voter registration prior to the turn of the century, it abolished it in 1951. The state relies on small electoral precincts, where the election boards running the polls know the voters. 8. When George Washington was elected as the first president in 1789, only six percent of the US population could vote. 9. US elections are not decided with a popular vote, but by a group of officials know as the 'electoral college'. Each state has the same number of electors as it has congressmen and senators, with three more for Washington DC. The candidate who gets over half of the votes in the electoral college is declared the winner after the college meets at the start of December. 10. There have been four occasions when the presidential candidate with the most votes did not gain office. The most recent example was in 2000, when George W Bush polled half a million votes less than Al Gore, but still managed to gain more votes in the electoral college. 11. Two elections in US history have had to be decided by the House of Representatives, when no candidate received enough support in the electoral college. In these cases, each state delegation gets one vote to cast for one of the three candidates who received the most electoral votes. 12. George Washington is the only president to receive all the votes in the electoral college, and he's also the only one to not belong to a political party. 13. There have been presidents from six political parties in the history of the USA: Democratic-Republican, Democrat, Federalist, National Union, Republican and Whig. 14. Since 1872, the US has elected either a Democratic or a Republican party member to the highest office in the land, though there are many more political parties in the US, with the Green Party, the Libertarians, the Constitution Party, and the Natural Law Party among them. 15. There are only three criteria a potential presidential candidate needs to meet – they must be a 'natural-born' US citizen, be at least 35 years of age and have lived in the US for at least 14 years. 16. Ahead of this year’s election, over 1800 people registered as potential presidential candidates with the Federal Election Commission. 17. Candidates who don't get the nomination of a political party can stand as an independent and petition each state to be added to the ballot paper by collecting a number of signatures from voters in that state. The number required is set by the state and can be as few as 275 votes in Tennessee, or as many as 178,039 in California. 18. All but nine states also permit 'write-in' candidates, who don't appear on the ballot but attempt to get enough supporters to write their names on the voting form in place of the official candidates. 19. South Dakota and Texas have presidential 'sore loser' laws which prevent people who failed to secure the nomination of a political party from running as independents or write-in candidates. 20. Potential presidential candidates announce their candidacy well in advance of the election – the first this year was Senator Ted Cruz of Texas, 596 days before election day. The earliest announcement ever was Mike Gravel, an ex-senator from Alaska, who put himself forward over 900 days before the election. 21. Modern US elections are generally determined by 'swing states', a small group of about a dozen states that sometimes vote Democrat and sometimes vote Republican. Candidates will focus their time, money and resources on winning these swing states and voters there are bombarded with advertising and endless visits from the candidates.