How does the US election actually work?

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US presidential nominees Donald Trump and Hillary Clinton had their third and final debate on Wednesday night, and now we wait until November 8 to find out who is the new commander-in-chief of the world's largest economic power.

So how does the presidential election work, and how does it compare with the UK's political system?

Who is involved?

Hillary Clinton and Donald Trump
Hillary Clinton and Donald Trump are heavily involved - you may have noticed (PA)

Presidential candidates must be natural-born citizens of the US, an American resident for the past 14 years, and aged over 35.

This year Trump, 70, is the Republican presidential nominee, while Clinton, 68, is in the same position for the Democrats. Each candidate also has a running mate - their nominee for vice-president - and Trump chose governor of Indiana Mike Pence while Clinton chose Virginia senator Tim Kaine. As a duo, the presidential nominee and their running mate is known as a ticket.

Trump shakes hands with Pence
Trump and Pence are running mates, but not the jogging kind (Evan Vucci/AP)

In the UK, the Conservative and Labour parties dominate - but many seats in Parliament are taken up by other parties such as the Liberal Democrats and the SNP.

In contrast, the US Congress, their version of parliament, currently has only two delegates from other parties out of 535 - this is why you almost exclusively hear about the Republicans and the Democrats.

Other presidential nominees you may not have heard of include Jill Stein for the Green Party, Gary Johnson for the Libertarians, and Evan McMullin - an independent nominee backed by anti-Trump Republicans.

When does it all happen?

A sign displays absentee voting hours at a voting site in Marietta, Ga
Advance voting is available for election day absentees (Mike Stewart/AP)

Presidential elections occur every four years, with election day happening on the first Tuesday after the first Monday in November - this year that is November 8.

On election day, voters across the US choose a president and a vice-president, with the winner usually announced that night.  However, when they cast their vote they are actually voting for an elector, who vote on behalf of their voters during the Electoral College in December - we will explain this slightly bizarre process shortly.

Finally, after nearly two years since the start of campaigning, on January 20 the new president is inaugurated.

MIchelle and Barack Obama dance on a United States President sign
Barack Obama shared a dance with his wife Michelle as he was inauguration for a second term in January 2013 (Evan Vucci/AP)

The presidential process started in spring last year, when candidates such as Trump and Clinton announced their intention to run for the White House. Following this, the candidates campaign, attend debates and hold primaries - lower level elections by party members which eliminates the weaker candidates.

There are tight limits on campaign spending for a general election in the UK, but US presidential candidates are allowed to spend big. The Washington Post reported in August that Clinton had raised $795 million (£647m) and Trump $403m (£328m) to spend on their promotional campaigns. In contrast, only £31.1m ($38m) was spent by all parties during the whole of the UK's 2010 election.

This graphic shows which
This graphic shows which 'swing states' may decide this year's results (PA Graphics/PA)

At each party's national convention, they vote for a nominee. This was when Republican voters chose Trump over party hopefuls such as Ted Cruz, and Democrats chose Clinton over Bernie Sanders.

How does voting work?

US presidential election: latest polls
The latest polls don't make for good reading for Trump, who has already claimed the election is 'rigged' (PA Graphics/PA)

A first-past-the-post electoral system in the UK sees voters choose the candidate they want to become their MP, and the candidate with the largest number of votes takes the seat in the Commons. The leader of the party with the most seats becomes Prime Minister.

The US presidents aren't directly elected by the people. Voters choose their presidential candidate but electors hold the power, as written in the US Constitution. During the Electoral College, electors cast votes, generally based upon which nominee received the most support in the public vote.

Map showing number of Electors in each state
This map illustrates the number of electors each state has (USAGov)

Electors are not required by the constitution to follow the popular vote, but it's rare for them not to do so. These votes are then counted by Congress and the candidate who has more than half, which is at least 270, wins. If no candidate receives a majority, Congress chooses one.

The number of electors each state has is roughly based upon population and equivalent to the number of seats in the two houses of Congress, plus three extras from Washington DC the US capital.

The latest projection of the result of the US presidential election
This graphic shows the latest projection for this year's election, with the candidates in their parties' customary colours (PA Graphics/PA)

What are the two houses?

Capitol building in Washington
The US Capitol building in Washington (Pablo Martinez Monsivais/AP)

US Congress has two houses - the House of Representatives, which makes laws like the UK's House of Commons, and The Senate, sometimes called the "upper house", which scrutinises new laws - like the House of Lords. Distinct from the UK however, elections are held for both houses while the presidential race is a third separate election entirely.

These houses are worth mentioning as the new president will want Congress to be largely populated by their own party - there are first-past-the-post elections for these every two years - otherwise they may struggle to pass new laws. This is a problem Democrat President Barack Obama has faced in his time in office due to the high number of Republicans in Congress.

How is the president different to the PM?

David Cameron (right) holding a joint press conference with US President Barack Obama
The US president and British PM, such as Barack Obama and David Cameron here, have a similar but distinct position (Ben Stansall/PA)

In the UK, the head of state is the Queen while the head of government is the Prime Minister. But in the US, the president is both.

Because the president is an elected position, they can make more decisions on their own. But in the UK, much of the PM's power rests in the size of their support in parliament. A PM's Cabinet is generally made up of MPs, but a president can technically choose anyone for their top table, as long as Senate confirms the appointment.

Barack Obama makes a statement at the start of a cabinet meeting
Clinton was appointed to Obama's cabinet in 2009, then as Secretary of State (Susan Walsh/AP)

Like the PM, the president's job is to set the political agenda, make sure laws are administered and to manage their country in a crisis.

However, deciding whether Trump and Clinton are quite up to doing so is perhaps beyond the remit of this humble explainer.