NEW YORK (AP) — Robert F. Kennedy Jr., an anti-vaccine conspiracy theorist and scion of the storied Democratic dynasty, is expected to launch an independent or third-party presidential bid on Monday. Cornel West, a philosopher and Black social leader, made the same choice last week. And No Labels, a new political party, is intensifying candidate recruitment efforts.

While the politics are murky, the fresh frenzy of outsider candidates threatens to weaken both major parties as President Joe Biden and Republican Donald Trump tighten their grip on their party's presidential nominations.

There’s little concern that the independent or third-party candidates would actually win the presidency, but they could siphon support from the ultimate Democratic and Republican nominees. A heightened sense of concern is spreading especially among Democratic officials, who see the outsiders as a dangerous wildcard that harkens back to 2016, when Green Party nominee Jill Stein may have enabled Trump’s razor-thin victory by winning a small portion of the vote.

Those associated with the third party efforts make no apologies for their work.

“The American people have been hungry for options. So, get ready,” Stein said in an interview. “What we’re seeing is a voter rebellion. It’s been a long time coming.”

The rise of outsider candidates is an acute reminder of the intense volatility — and uncertainty — that hangs over the 2024 presidential election. Both of the major parties' most likely nominees — Biden and Trump — are extraordinarily unpopular. They’re running as the nation grapples with dangerous political divisions, economic anxiety and a deep desire for a new generation of leadership in Washington.

Much more activity is expected soon.

Kennedy will outline his plans in Philadelphia on Monday. Stein said the Green Party will likely make an announcement about its presidential aspirations later this month. No Labels, meanwhile, plans to make a formal decision about its presidential nominee in the spring.

The efforts face steep hurdles beyond winning more than a small fraction of voters. Simply qualifying for the ballot in every state will be a gargantuan task for outsider candidates without the benefit of existing political networks.

Jim Messina, who managed President Barack Obama's 2012 reelection campaign and is now a prominent Biden ally, didn't downplay the possibility that the new candidates could weaken Biden's coalition.

“I am a campaign manager so I am wired to plan for everything and panic about nothing, and the threat of a third party needs to be planned for seriously,” Messina said.

Noting that no independent or third-party candidate has ever won even a single electoral vote — never mind the 270 needed to claim the presidency — he said Biden and his team still need to be aggressive in warning voters about the threat that long-shot outsider candidates present.

“You need to tell people that a vote for a candidate without a path to 270 means they’re lighting their ballot on fire,” Messina said.

That may be easier said than done.

Gallup released new polling last week showing that 63% of U.S. adults currently agree with the statement that the Republican and Democratic parties do “such a poor job” of representing the American people that “a third major party is needed.” It was among the highest figures since Gallup first asked the question in 2003.

Still, it's far from certain that dissatisfied voters would ultimately cast a ballot next fall for Kennedy, West or a centrist No Labels candidate. Historically, polls showing that people want a third party to exist have rarely translated into substantial support for actual third-party candidates.

On paper, Kennedy may be most likely to draw support from Trump's coalition given his embrace of anti-vaccine conspiracy theories and positive attention from far-right media.

Aware of the risk, Trump allies have begun circulating opposition research against Kennedy designed to damage his standing among would-be conservative supporters. In addition to highlighting his past support for Hillary Clinton's Senate and presidential campaigns, Trump allies in recent days have also circulated a pre-pandemic video clip of Kennedy declaring himself “fiercely pro-vaccine” in a message to Black religious leader Louis Farrakhan.

Kennedy campaign spokesperson Stefanie Spear said the clip has “obviously been removed from its context.”

“Mr. Kennedy is and has always been against mandates for any and all medical interventions," she said. “Mr. Kennedy’s position is that he is in favor of vaccines that have undergone unbiased scientific testing for safety and efficacy. Such testing has been impossible because of the corrupt influence of the pharmaceutical industry."

Trump senior adviser Chris LaCivita downplayed any internal concerns about Kennedy's impact on the race.

“The most intriguing thing about this is, you have an incumbent president of the United States, and all of the elements of the third-party run are coming out of his coalition, not ours,” LaCivita told The Associated Press.

The Trump and Biden campaigns are quick to note that it will be very difficult, if not impossible, for the political outsiders with no major funding sources or political infrastructure to get their name on the ballot in most states. No Labels is the big exception, having already secured a presidential ballot line in 11 states backed by an army of paid signature collectors.

In Arizona, alone, minor party candidates must collect more than 34,000 signatures to qualify for the general election ballot. Signatures must be collected in at least five different counties, and at least 10% of signatures must be from counties with populations of less than 500,000. An independent candidate must collect more than 43,000 signatures.

Michigan requires a minor party candidate to collect 44,619 signatures and independents to collect 12,000. And in Nevada, a minor party or independent candidate must collect 10,095 signatures to qualify for the ballot. At least 2,524 signatures must be collected in each of Nevada’s four congressional districts.

But an outsider candidate does not need to qualify for the ballot in every state to have a profound political impact. Just ask Brendan McPhillips, the state director for Biden's Pennsylvania efforts in the last election.

Like many Democrats, he still blames Stein for helping Trump win the battleground state in 2016. While it's impossible to say for sure, Trump carried Pennsylvania that year by just 44,000 votes, while Stein, an outspoken progressive, won nearly 50,000 votes in the state.

“It’s dangerous," McPhillips said of the independent and third-party candidates. “But I also think the Biden campaign is going to be smart about this. They’re going to make sure everybody knows the consequences of throwing your vote away on some egomaniac's vanity project.”

For now, Biden's team has allowed two Democratic-aligned groups, MoveOn and Third Way, to take the lead in public attacks against the outsiders. Leaders from the groups recently hosted private briefings with senior aides on Capitol Hill to raise the alarm about No Labels especially.

Third Way co-founder Matt Bennett said Kennedy is also a problem.

“Anything that divides the anti-Trump vote is dangerous,” Bennett said. “Kennedy divides it on the fringes. And No Labels divides it from the center. ... It's seriously worrying.”

Anxious Democratic officials comfort themselves by pointing to a trend in recent elections in which young people and suburban women have turned out in strong numbers for Democratic candidates. But looking to 2024, recent polls suggest that a Trump-Biden rematch would be competitive.

The 2024 outsiders likely won't make it any easier for Biden.

In fact, they're actively challenging his core message on democracy, which the president's team says is essentially on the ballot next fall as Trump and his supporters undermine the rule of law and integrity of the vote.

“We are out there proudly giving people a choice and fighting for real democracy, not the democracy where the Democratic Party says, ‘Yeah, we’re saving democracy from the Republican Party by squelching any chance of a primary, by shaming voters who want to vote for a third party or an independent,’' said West's campaign manager, Peter Daou. ”No, the true fight for democracy is to finally give people choices."

And while West will rely on grassroots volunteers and small-dollar donations to secure his place on the November 2024 ballot, the No Labels movement is making almost exactly the same argument and is backed by tens of millions of dollars in anonymous donations.

In an interview, former Connecticut Sen. Joe Lieberman, the No Labels founding chairman, said the organization will begin a candidate recruitment and selection process in the next two to three weeks. The group would decide to move forward with a centrist candidate, he said, only if Biden and Trump appear likely to win their party's presidential nominations after the batch of primary contests known as Super Tuesday next March.

A final decision will be made by delegates at a convention scheduled for April in Dallas, but a process for choosing those delegates has not been announced.

“The parties have such a stranglehold on American politics and government for too long and it’s really hurting our country,” Lieberman said. “The public is crying out for a third choice, and maybe we need to listen to the public."

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AP writer Jonathan J. Cooper in Phoenix contributed.