Despite all the talk of democracy, US voters do not technically elect their president. Instead, the results of the general election will, like all presidential contests, merely provide a guide for Electoral College members. They, in turn, pick the winner.
Usually it is little more than a procedural difference, but that was not the case in the 2000 election.
Democrat Al Gore received more of the popular vote, but Republican George W Bush got the Electoral College's nod after the US Supreme Court shut down the Florida recount.
How this uniquely American voting system works:
There are 538 popularly-elected members of the Electoral College, allotted to each of the 50 states and the District of Columbia based on their representation in the US Congress. The smallest states have three members while the largest state, California, has 55.
This ends up giving smaller states much more power as the proportion of members does not equal the proportion of population. Washington DC, which has no representation in Congress, has three members, the same as the smallest states.
It takes 270 electoral votes to win election. The electors are pledged to one candidate or the other but there is no federal law requiring them to vote that way.
There have been several incidents in which a 'faithless elector' has voted for someone other than the major candidates. However, in 2000, the Florida electors stuck by the decision of the US Supreme Court even though they had the power to give Al Gore the victory.
In 48 states and the district, the candidate who wins the popular vote wins all of the state's electors. Nebraska and Maine have a proportional system of awarding electors.
Electors, who are picked by the respective political parties, make two selections - for president and for vice president. They may not vote for two candidates from their own state.
Because a candidate could run up a big vote count in some states but lose others by narrow margins, the winner of the popular vote might not have the most electoral votes.
The Electoral College has three times picked the candidate who lost the popular vote: Republicans Rutherford B Hayes in 1876, Benjamin Harrison in 1888 and George W Bush in 2000.
If no candidate receives a majority of the electoral votes, the House of Representatives chooses among the top three candidates with each state having only one vote. If no vice presidential candidate receives a majority, the Senate decides between the top two candidates.
The House has twice decided the outcome of the presidential race, in the 1800 and 1824 elections. The Senate decided the vice presidency once, in the 1836 election.
This unique system was the result of a compromise by the writers of the US Constitution in the 18th century between those who wanted direct popular election and those who wanted state legislatures to decide. One fear was that at a time before political parties, the popular vote would be diluted by voting for an unwieldy amount of candidates.
The real battle is for the "swing states" - those where the outcome is uncertain – Arizona, Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, North Carolina, Ohio, Pennsylvania, Virginia, and Wisconsin.
Together these states have 157 electoral votes up for grabs. Whoever can carry enough of those states to bring the overall electoral vote total to at least 270 will win.
US presidential election in numbers pic.twitter.com/nrryiPzaMq— RTÉ News (@rtenews) November 7, 2016
A candidate can win the most votes nationally and still lose by failing to accumulate a majority of electors.
The biggest Electoral College prizes are California with 55 votes; Texas with 38; and New York and Florida, each with 29.
In what is largely a formality long after the winner has been determined, each state's electors will meet on the Monday after the second Wednesday in December (19 December) in their home states and cast their votes for president and vice president.
Congress will meet on 6 January to conduct an official tally.
The President-elect takes the Oath of Office and becomes the 45th President of the United States at noon on 20 January 2017.