Green Party presidential nominee Jill Stein and Libertarian Party nominee Chase Oliver haven’t been getting much attention lately, but that could all change on Tuesday.

The duo and other alternative presidential candidates — including ex-candidate Robert F. Kennedy Jr. — could tip the results in deadlocked battleground states and play a deciding role in who wins the White House.

Ms. Stein is on the ballot in 39 states, including six of the seven battleground states expected to decide whether Vice President Kamala Harris or former President Donald Trump gets the Oval Office job.

Ms. Stein has weathered sharp criticism from Democrats that she’ll spoil the race for Ms. Harris, especially in the must-win battleground of Pennsylvania.

She’s even getting last-minute pressure to drop out and endorse Ms. Harris from the European Greens, a coalition of left-wing environmentalist groups across Europe. They are terrified she’s aiding and abetting Mr. Trump.

“We face a climate crisis that is worsening every year [and] climate policies require democratic institutions, which we fear would be dismantled if Trump is elected,” said the group, which includes Green parties from Belgium, Denmark, France, Germany, Ireland, the Netherlands, Poland and Ukraine.

Ms. Stein said she wouldn’t drop out.

She is running as an alternative to both Mr. Trump and Ms. Harris on an anti-war, anti-fossil fuels platform. She promised to cut off military aid to Israel in its war with Gaza if a cease-fire deal is refused.

Her stance also threatens to draw pro-Palestinian voters away from Ms. Harris, who has lost some ground on the left because of her support for Israel.

“The votes of the opponents of genocide are not being taken from Kamala Harris,” Ms. Stein told CBS News in Pittsburgh. “She already lost them.”

Mr. Oliver rejected accusations he’s a spoiler. He is running as an anti-war, pro-free trade candidate who wants to lessen government intrusion. He condemned the two-party system that claims a vote for him is wasted. 

“This is the establishment’s most successful lie in modern politics,” Mr. Oliver said in a campaign advertisement. 

Polls show Ms. Stein drawing up to 2% of the vote in six swing states. It seems like a minuscule number, but those polls predict she could siphon away just enough from Ms. Harris to tip a close race to Mr. Trump.

Mr. Trump also faces threats from third-party candidates, including Mr. Kennedy, who quit the race in August and is now a Trump campaign surrogate.

Mr. Kennedy, who started as a Democratic Party candidate and then switched to indpendent before dropping out, failed in his attempts to extricate himself from two swing state ballots. Despite his arduous public support of Mr. Trump, who has promised him a role in a Trump administration, his name remains on the ballot in Michigan and Wisconsin, where he is expected to cannibalize some Trump votes.

Then there’s Mr. Oliver. He is unknown to most voters, but he’ll appear on ballots in 48 states, including every battleground state. He attracted less than 1 percent in most polls, but added together with Ms. Stein and Mr. Kennedy, the threesome threatens to shake up the results. 

“If a state is close enough,” nonpartisan pollster Ron Faucheux said, “their vote could determine who wins it.” 

The latest polling in Wisconsin, published Wednesday by Marquette Law School, shows Mr. Kennedy’s lasting impact on the race.

A head-to-head matchup found Ms. Harris leading Mr. Trump 50% to 49%. Her lead over Mr. Trump widens to 46% to 44% when the poll factors in all the candidates, particularly Mr. Kennedy, who picked up 5% of the vote. 

In the same poll, Ms. Stein won 1% of the vote, Mr. Oliver got 2% and independent Cornel West received another 1%. 

Nearly 10% of Wisconsin’s presidential vote will go to third-party and independent candidates, the Marquette Poll found. 

David Paleologos, director of the Suffolk University Poll, one of the most accurate in the country, predicted the impact of the alternative candidates could be “very big.”

Ms. Stein was a spoiler in 2016, when, along with Libertarian Gary Johnson, they garnered more votes in the three “blue wall” states of Michigan, Wisconsin and Pennsylvania than the margin of Hillary Clinton’s loss to Mr. Trump.

In 2020, Libertarian Jo Jorgensen, the only significant third-party candidate on the ballot, may have hurt Mr. Trump. He received more votes than the margin by which Trump lost in Georgia, Arizona and Wisconsin. 

Other past spoilers include Ralph Nader, who in 2000 may have robbed Vice President Al Gore of a win in the then-swing state of Florida. Ross Perot, who picked up nearly 20% of the popular vote in 1992, drew most of it away from President George H.W. Bush, who lost to Bill Clinton.

A Suffolk Poll released on Friday showed Pennsylvania deadlocked. Mr. Trump and Ms. Harris each garnered 48.6% of the vote. Combined, Ms. Stein and Mr. Chase were backed by just 1% of Pennsylvania voters, but it could be enough to sway the race.

In 2020, President Biden beat Mr. Trump in the Keystone State by 1.17%.