In several swing states, the polls for the 2024 election are virtually undecided. The smallest factor could influence the results in either case — including the presence of a third-party candidate on the ballot.

Third-party candidates typically don't have much appeal: Without a major party behind them, every step of the electoral process is significantly more difficult, including building name recognition, gaining endorsements, getting on the ballot or in a debate, and fundraising.

But third-party candidates don't need a lot of support to upset a race. In the last two election cycles, the average number of deciding votes in the seven swing states was less than 125,000 votes. In Wisconsin, for example, the election went for Trump by 22,748 votes in 2016 and for Biden by 20,682 votes in 2020 – an average margin of less than 21,715 votes. And while it is unlikely that any third-party candidate alone will exceed this threshold, the votes of all third-party candidates combined have significantly exceeded this threshold in some states.

Kyle Kondik, editor-in-chief of Sabato's Crystal Ball at the University of Virginia Center for Politics, said the third-party vote share this year is likely to be closer to what it was in 2020 (about 2 percent) than what it had in 2016 (about 2 percent). 6 percent). That could be in part because an unusually large share of Americans were dissatisfied with their presidential options in 2016, and Harris' entry into the race to succeed President Joe Biden this year appears to have given most Democratic-leaning voters a candidate to have something to stand behind.

Still, Kondik said it is “possible, if not likely, that the overall third party share will be greater than the margin between Trump and Harris in one or more states.”

This means that third-party voters, who are notoriously unpredictable and difficult to persuade, could play a crucial role in a very close election, swaying it in either Trump's or Harris's direction.

Who are the third-party candidates on the ballot?

There are some key third-party candidates you should know about. None of them are very popular, but together the top four are around 3 percent nationally. (Notably, Harris and Trump are within 2 percentage points of each other by most polling averages and models).

Prominent among the third-party candidates sweeping swing-state votes this year is the Green Party's Jill Stein, a progressive who attracted Democratic-leaning voters in her last two presidential runs.

Stein is running in every swing state except Nevada and is supported in Michigan by a Muslim American group called Abandon Harris. The vice president is battling Arab American voters there who contributed to Biden's victory in 2020 and who reject the Biden administration's approach to the war in Gaza.

Both Stein and Libertarian Party candidate Chase Oliver each claim about 1 percent support nationally, according to a recent New York Times poll. That's less than Stein's vote share in 2016, when she last ran for president.

Still, it could be enough to skew results in the same states where she has previously won significant numbers of voters: In 2016, she received more votes in the blue wall states of Michigan and Wisconsin than Trump won in those states could.

Another potential wild card in these states is independent Robert F. Kennedy Jr., who suspended his campaign in August and endorsed former President Donald Trump.

He was once seen as a potential spoiler for both Trump and President Joe Biden, given his support for the anti-establishment views of certain parts of the Republican Party and his status as a member of the Democratic Kennedy dynasty. Kennedy was around 10 percent nationally for most of 2024, and even higher in some swing state polls. But his support fell to less than 5 percent in August after Harris took the Democratic nomination, suggesting that many Democrats saw him as the only alternative to Biden and were not particularly interested in his candidacy.

Now he has more potential to spoil Trump. According to the New York Times, recent polls put him at about half a percentage point, tied with the independent Cornel West.

Although he managed to withdraw from the ballot in Georgia, North Carolina, Arizona and Nevada, he is still on the ballot in Wisconsin. The Wisconsin Supreme Court decided to keep him there on the ballot, but he has appealed that decision. It is unclear how, from a practical perspective, the court could make a decision in his favor; Almost 100,000 people have already received mail-in ballots with his name on them.

A federal judge also ruled that Kennedy must remain on the ballot in Michigan, where the race has narrowed and Harris now has less than a percentage point lead in the FiveThirtyEight polling average.

Other third-party candidates include Claudia De la Cruz of the Socialism and Liberation Party, Joel Skousen of the Independent American Party, Randall Terry of the Constitution Party and Joseph Kishore of the Socialist Equality Party. However, none of them have the support that the above four have received.

Together, these third-party candidates have some potential to reduce Harris and Trump's electoral margin in states where they need to win. Although third-party candidates often appear to be stealing votes from the two major party candidates, the election results may not be different if they were not on the ballot.

“Third-party voters can be quirky and are not particularly attractive to either campaign — perhaps some of them would not have voted for the majority party even if those were the only options,” Kondik said.