Third-party candidates appear to be playing more of a "spoiler" role against Hillary Clinton than Donald Trump, according to most polls. With the exception of the Los Angeles Times/USC Tracking poll, which has consistently favored Trump, most head-to-head polls have Clinton with a larger margin of victory over Trump than in four-way races.

In a recent Reuters/Ipsos poll, Clinton received 44 percent compared to 37 percent for Trump in a two-way race amongst like voters. In a four-way race amongst likely voters, Clinton also leads but by a slimmer margin: 42 percent to 36 percent.

Among registered voters, Clinton owned an even wider lead over Trump in a head-to-head race, 47 percent to 34 percent. But in a four-way race, Clinton leads Trump, 44 percent to 33 percent. 

While the margins are minor—Clinton's lead is only trimmed 1 percentage point among likely voters and 2 points among registered voters—the Clinton campaign may be worried that support for the Libertarian Party and the Green Party, combined with possibly lower voter turnout, could swing the election to Trump.

In a highly unconventional election cycle, even small margins in polls could spell doom and the threat of third-party competitiveness could prompt a scenario like the 2000 election. Democratic nominee Al Gore finished four electoral votes short of the 270 needed, while Green Party nominee Ralph Nader received 97,488 votes in Florida and 22,198 in New Hampshire—two states that would have swung the election to Gore.

The third-party candidates appear to be seizing on voter dissatisfaction, despite an increasingly bleak shot at winning the general election. Green Party nominee Jill Stein, who has polled at just 2.4 percent in a Real Clear Politics average poll, has actively pursued Democratic supporters of Vermont Sen. Bernie Sanders.

“We’re picking up where Bernie left off," Stein told the Washington Post in July. "In fact, you could say we were here back in 2012 doing the same thing, long before Bernie’s campaign.”

And while Libertarian nominee Gary Johnson, a former two-term Republican governor of New Mexico, would appear to be a candidate that would draw support from Trump due to similar stances on economic issues, he has actually drawn young voters who are often more inclined to vote for a Democrat.

According to a New York Times/CBS News poll in Septemeber, 26 percent of voters ages 18 to 29 said they plan to vote for Johnson, while 10 percent backed Stein. 

Johnson, meanwhile, is expected to outperform his 2012 campaign. He is currently polling at about 7 percent after receiving 0.99 percent in the last election.

But the swing states mean more than the general-election poll numbers. In Ohio, arguably the most contentious battleground state, Trump leads in six of the last eight polls, by no higher than five percent. Meanwhile, Johnson polls as high as 10 percent while Stein polls as high as 3 percent.

In September, Peter Brown, Assistant Director of the Quinnipiac University Polling Institute, raised the importance of Johnson's role in Ohio when the Libertarian received his highest level of support in the state. 

"Libertarian Gary Johnson could decide the presidential election in the Buckeye State," Brown said. "He is getting 14 percent from Ohio voters and how that cohort eventually votes could be critical in this swing state – and in the nation."

Also in September, Stein drew headlines for flying into Cincinnati instead of Columbus for a campaign event. But the snafu didn't detract from the fact that she was seeking votes in a state that means so much to the two major parties. According to her official website, Stein has upcoming events in four California cities: Northridge, Oakland, San Francisco, and Santa Barbara. Clinton is currently leading Trump in California by nearly 20 points.