Six months ahead of the US presidential election, Donald Trump is already the presumptive Republican candiate while Hillary Clinton moves ever closer to securing the Democratic nomination.

However, there are far more canidadates than Trump and Clinton hoping to have their names on ballots in November - and we're not just talking about Bernie Sanders.

In the classic Simpsons episode Treehouse of Horror VII - originally broadcast only days ahead of the 1996 US presidential election - the aliens Kang and Kodos impersonate presidential candidates Bill Clinton and Bob Dole in a bid to take control of Earth. When Homer finally reveals the true identity of the candidates, the two aliens insist they’re likely to win the election anyway as “it’s a two party system - you have to vote of one of us”.

One member of the gathered crowd suggests he’ll vote for a third-party candidate instead. “Go ahead, throw your vote away,” Kang responds, followed by plenty of evil cackling. In one of the great Simpsons endings, Kang wins and goes on to enslave the population of the US.

The Simpsons scene - probably one of the best examples vintage Simpsons writers' incredible capacity for sharp and hilarious political satire - makes an unexpected appearance in a campaign clip for US presidential hopeful John McAfee. So too does an extended clip from the sci-fi cult classic Serenity. The rest of the loud, visceral and aggressively untraditional campaign video lays out McAfee’s political ideology and distrust of the established system.

People with epilepsy beware - this video contains plenty of flashing images.

If the video didn’t make it abundantly clear, McAfee - best known as the founder of the computer security firm that bore his name, and for his rather eccentric behaviour in recent years - is a libertarian. He’s seeking the nomination for the Libertarian Party - the party that favours ‘minimum government’ and ‘maximum freedom’.

The party says it is neither liberal nor conservative - it favours “lowering taxes, slashing bureaucratic regulation of business, and charitable - rather than government - welfare”, but also describes itself as ‘socially tolerant’.

McAfee is looking unlikely to secure the nomination over frontrunner Gary Johnson at the party’s national convention later this month. Mr Johnson - a former Governor of New Mexico - was the Libertarian candidate for the 2012 election. He won 0.99% of the popular vote. However, polls suggest he could make major gains in this year’s election - a survey from Morning Consult puts him at 10% support nationally, compared to 38% for Hillary Clinton and 35% for Donald Trump.

If he managed to secure that level of support in the election, it would easily make Gary Johnson the most successful third-party candidate since Ross Perot in the 1992 election. If he makes it to 15% support in coming months, Johnson would earn himself a place on the televised presidential debates (he is already campaigning to have the 15% restriction overturned).

Alongside the Libertarian hopefuls in this election, there’s plenty of others hoping to have their names on the November ballot paper. The country’s Green Party will put forward a candidate, with Jill Stein looking likely to secure the nomination. She was the party’s candidate in 2012 - while she only received 0.36% of the vote (just under 470,000 votes), it was a performance that handed her the record for most votes ever received by a female candidate in a US presidential election.

The Greens managed their best ever performance in 2000, where Ralph Nader managed to win 2.88 million votes. However, Nader’s performance became somewhat infamous, amid a debate on whether or not his votes in Florida ‘spoiled’ the result by helping George W Bush achieve a narrow victory over Al Gore.

Alongside the Greens and Libertarians, a number of smaller parties and groupings are also putting candidates forward. Some are very specific, such as the Prohibition Party and the Nutrition Party. The Prohibition Party - which boasts that it has “opposed the manufacture, distribution, and sale of alcoholic beverages since 1869” - received a total of 518 votes in the 2012 vote. Many of the smallest parties only have access to ballots in a few - if any - States.

Barriers to the presidency

Traditionally, third parties have struggled in all US political elections. For example, there are currently only two US senators not associated with either the Republicans or Democrats - Angus King and Bernie Sanders. Sanders is, of course, seeking the Democratic nomination for the presidency, and has therefore been a member of the party since last year - although he was elected to the senate as an independent.

In a presidential race, the most successful third-party candidate in modern history (ever since the formation of the Republican and Democrats) was Theodore Roosevelt in 1912, who ran for the then newly formed Progressive - or ‘Bull Moose’ - Party. Roosevelt, who had been President between 1901 and 1909, formed the party after losing the Republican nomination to William Howard Taft.

Roosevelt secured 27.4% of the vote - beating his rival Taft, but falling well short of Woodrow Wilson’s winning performance. Perot’s 18.2% as an independent in 1992 is the strongest performance by a non-Republican / Democrat since Roosevelt’s unsuccessful bid.

Third-party candidates in the US unfortunately have a number of factors working against them. The country’s national electoral systems are not based on proportional representation, meaning candidates from smaller parties and independents face a significant barrier in overcoming the established parties in a race to be ‘first past the post’. In fact, strict electoral ballot laws in different states mean that many small parties cannot fulfill the criteria to appear on ballots in the first place.

It is likely that a fundamental change to existing systems and a very high-profile candidate would be required to really allow a third party to ‘break through’ and overcome the deeply ingrained Republican and Democratic dominance. 

So do US voters, as Kang suggested, really face a choice between the GOP, the Democrats or throwing their votes away?

Even if a favoured candidate is unlikely to win, a vote for them could be seen as a rejection of the mainstream candidates. It is a clear way to put forward 'protest vote'. In an ideal world, third-party candidates would help at least influence the agenda: significant support for the Green Party, for example, may show a public appetite for a new approach to environmental issues. And it’s fair to say that if people remain reluctant to vote for a third party, then the system is going to keep favouring two main parties.

A recent Washington Post poll has shown that 44% of respondents want another choice in a now almost inevitable Trump-Clinton face-off. The appetite is definitely there for a third party, and anti-establishment sentiment seems higher then ever. Bernie Sanders running as an independent candidate would definitely have a major impact - but he has ruled it out.

If this is unlikely, then, to be the election where the two party system is toppled, the campaign so far has shown in no uncertain terms that US politics still has plenty of capacity to surprise.