Florida voter Sabiha Kazi, 38, wants to get corporate money out of politics, but she does not believe any of the major party candidates will be able to achieve that.

"Both parties are in bed with large corporations," said the doctor, who is part of an anti-war women's peace group called Code Pink. "I voted Obama in 2008, but this year I will vote for Jill Stein."

Many like Dr Kazi who have low opinions of Republican candidate Donald Trump and Democratic candidate Hillary Clinton are turning to Libertarian Party candidate Gary Johnson or the Green Party's Dr Stein. And while these third-party candidates have little hope of winning, there is some talk of their potential as spoilers in this election.

A polling average by political website Real Clear Politics shows that Mr Johnson, a former New Mexico governor, has 9 per cent of the vote while Dr Stein has 3.3 per cent.

Mr Johnson was harshly criticised on Thursday after revealing a lack of knowledge of foreign affairs during an interview.

When asked on MSNBC about the crisis in Aleppo, the war-torn Syrian city, he asked: "What is Aleppo?" He later released a statement explaining that he is "human" and that he "blanked" when asked the question.

Some say this could derail his attempts to drum up enough support to make it to the debate stage with the two major candidates - he has to hit 15 per cent in major national polls to be included.

Still, support for Mr Johnson and Dr Stein is much higher than in 2012, when both candidates also ran for the presidency. Then, Mr Johnson received around 1 per cent of the popular vote while Dr Stein received just 0.36 per cent.

Professor John Clark, chair of the department of political science at Western Michigan University, said: "Both Donald Trump and Hillary Clinton have strong bases of support, but both of them have very high negatives too. In such circumstances, I would expect a larger-than-usual proportion of voters to look for some alternative candidates."

According to a poll this month by The Economist and market research firm YouGov, Mrs Clinton has an unfavourability rating of 54 per cent and Mr Trump's rating is 63 per cent.

Not since the 2000 election, when Green Party candidate Ralph Nader was accused of costing Democratic candidate Al Gore the presidency, has there been this much attention paid to minor parties.

In 2000, Mr Nader won 97,488 votes in Florida and Republican candidate George W. Bush won the state by 537 votes, according to the official Florida tally.

"Had only 1 per cent of Mr Nader's voters switched their vote to Democratic candidate Al Gore, Mr Gore would have been elected president," said Prof Clark.

Experts say there is not much data on who the third-party voters might be, but they tend to be young and "do not have a well-rooted sense of partisan identification".

"Some voters are also motivated to back Johnson or Stein on particular issues that are salient to them, for example, tax reform or drug policies," said Purdue University professor of political science James McCann.

He said Mr Johnson is pulling votes equally from Mr Trump and Mrs Clinton. Others have also pointed out that Vermont senator Bernie Sanders' supporters have shifted their loyalty to Dr Stein, who is filling the role of left-wing firebrand in this election.

"In a close election, it wouldn't require too many votes siphoned from one major party candidate to throw the election to their major party opponent," said Prof Clark. "This year's election doesn't seem to be that close at this point, but there is a lot of time between now and election day."