President Biden and former President Trump are likely to win their parties’ nominations. Yet a recent Associated Press-NORC poll found that 58% of Americans dislike the idea of Trump running again, and 56% are unhappy with Biden for staying in the race.

That gives an enormous amount of power to those who dislike both, the “double haters.”

That happened in 2016, when voters who disliked Trump and Democratic candidate Hillary Clinton broke in Trump’s favor. And again in 2020, when the double haters deserted Trump for Biden.

But this campaign has another wild card: independent and third-party candidates.

Early polls have found that when voters are offered a third choice, up to 17% grab it — enough to swing the election.

Those numbers don’t predict what will happen in November; in most years, the third-party vote shrinks rapidly as election day approaches. But they’re added evidence that voters yearn for choices different from the ones looming.

And that’s encouraged a burgeoning list of independent and third-party candidates: Robert F. Kennedy Jr., who made his name as an anti-vaccine militant; Cornel West, a prominent Black academic and socialist activist; Jill Stein, the probable third-time nominee of the Green Party; and perhaps most intriguing, a well-funded group called No Labels that hopes to field a ticket with a moderate Republican and a moderate Democrat.

That’s a problem for Biden more than Trump. Strategists in both parties believe some of the president’s current voters are more likely to desert him if they see an appetizing alternative. A Bloomberg-Morning Consult poll in seven swing states last month found evidence of that: 16% of Biden voters said they might vote for Kennedy or another independent candidate, while only 11% of Trump voters said they were tempted to take the third-party route.

Historically, no third-party candidate has ever won a presidential election, but several have succeeded in tipping the balance.

That happened in 1912 when Theodore Roosevelt, a former Republican running as the Progressive Party candidate, split the GOP vote and delivered the White House to Democrat Woodrow Wilson. And in 2000, when Democrat Al Gore lost Florida by 537 votes, arguably because Green candidate Ralph Nader collected more than 97,000 votes in the state. And in 2016, Hillary Clinton lost the key states of Michigan, Wisconsin and Pennsylvania by fewer votes than Stein collected in those states.

In last week’s average of polls compiled by the website Real Clear Politics, when voters are offered more than the two major-party candidates, Kennedy attracts about 14% of the national vote; West and Stein attract 2% each. (The No Labels proposal can’t be tested the same way because the group hasn’t named its candidates.)

The most important factor at this stage, however, is not those ephemeral voter preferences. It’s whether any of those third-party candidates can get on the ballot in the closely divided “battleground states” that will almost certainly decide the presidential election: Arizona, Georgia, Michigan, Nevada, New Hampshire, North Carolina, Pennsylvania, Wisconsin.

“The national numbers aren’t important,” said Doug Sosnik, a longtime Democratic strategist who worked for President Clinton. “All that matters is how these candidates are doing in the states that will decide the election. That’s where a few percentage points can decide the whole thing.”

That’s why many Democratic strategists worry most about No Labels, the well-funded group that has a head start toward getting on the ballot in all 50 states. So far, No Labels has won ballot access in 14 states, including the battlegrounds of Arizona, Nevada and North Carolina. Stein’s Green Party is likely to get on the ballot in most states too.

Kennedy has qualified only in Utah. West’s prospects are uncertain; it is unclear that he has the funding or organization to mount a nationwide ballot-access effort.

Last week Third Way, a centrist Democratic think tank, issued a new warning to Democratic donors to steer clear of No Labels.

“Their own polling says they’d lose and be a spoiler for Trump,” Third Way Executive Vice President Matt Bennett said in an email.

No Labels contests that assertion and says its polling suggests that it could win enough states with 34% or more of the vote to assemble an electoral college majority. Political pros consider those simulations far-fetched.

It still is unclear whether No Labels will run a ticket at all. The group planned a convention this summer, then scrubbed it.

Still, if any of those third-party candidates get on the ballot in battleground states, they’ll present an added burden for Biden.

When a president runs for a second term, the election is normally a referendum on his record. Biden hopes to flip that script and win by turning the election into a referendum on Trump. Third-party candidates could disrupt that by offering anti-Trump voters an escape route.

That means Biden won’t be able to win solely by stoking fears of his predecessor’s return. He’ll need to present a solid case that the third-party escape route is just another way of electing Trump.