Robert F. Kennedy Jr.’s presidential campaign was once viewed as a quixotic quest by a scion of a storied political family — an environmental warrior who sullied his family’s name most recently by aligning himself with a political party founded by a segregationist to get on the November ballot in California.

But a combination of voter apathy about President Biden and former President Trump, the two main parties’ presumptive nominees, and the Kennedy campaign’s successful targeting of ballot qualification rules across the nation has prompted growing alarm among Democrats and Republicans alike.

“When you have nail-bitingly close elections, nearly any candidate can be a spoiler,” said Thad Kousser, a political science professor at UC San Diego. “Now, the interesting thing, unlike a Jill Stein [a perennial Green Party candidate], it’s not 100% clear which major party candidate he hurts most. That uncertainty is going to lead to a lot of churning on what the parties do … to keep him off the ballot.”

Kennedy, the son of Sen. Robert F. Kennedy (D-N.Y.) and nephew of President John F. Kennedy, has no real chance of being elected to the White House in November. However, the Californian could be a spoiler in the race, tilting the vote. Two names are frequently raised: H. Ross Perot in the 1992 race and Ralph Nader in 2000, though there is debate about how much their candidacies resulted in Bill Clinton and George W. Bush winning their respective elections.

Kennedy has qualified to appear on the ballots of three states, most recently California, and his campaign claims to have collected enough signatures to appear on the ballots of seven others, including Nevada.

In California, the American Independent Party submitted paperwork to have Kennedy appear on the ballot as its standard-bearer, the candidate announced this week.

George Wallace, a segregationist Alabama governor who opposed federal civil rights laws, helped found the party and ran on its ticket in the 1968 presidential campaign. Kennedy’s father, a staunch supporter of such rights, was assassinated in Los Angeles during that campaign.

Leaders of the party, which currently exists only in California, say it has disavowed its segregationist roots and is focused on conservatism and the Constitution. In a video Kennedy released Tuesday, he called Wallace a “bigot” who “was antithetical to everything my father believed in.”

Mainstream Democrats are incredulous about Kennedy’s association with the party. When Wallace stood in a schoolhouse door at the University of Alabama, trying to block two Black students from registering, President Kennedy called in the Alabama National Guard at a time when his brother, Robert, was the nation’s attorney general.

Paul Mitchell, a veteran Democratic strategist, said he previously believed Kennedy had a shot of winning California based purely on his last name. That is no longer the case, based on how he has run his campaign and whom he has chosen to associate with, Mitchell said.

“If he was a Kennedy and acting like a Kennedy and professional, I wouldn’t put [a California victory] out of the bounds,” said Mitchell, who noted that Kennedy associated with the fringe party after gathering a paltry number of signatures for a political party he was trying to form. “Now he’s a loony anti-vaxxer conspiracy theorist and running a campaign like a loon. It’s so embarrassing.”

Biden supporters have been concerned about Kennedy for some time. The Democratic National Committee earlier this year established a team to oppose third-party candidates, chiefly Kennedy. Their first act was filing a Federal Election Commission complaint arguing that Kennedy’s campaign coordinated inappropriately with a Super PAC to qualify Kennedy for some states’ ballots.

“We know this is going to be a close election and we’re not going to take anything for granted,” said Matt Corridoni, a DNC spokesman working on the anti-third party effort, noting that the biggest donor to a pro-Kennedy PAC is a Trump mega-donor and that a New York-based campaign official pitched his candidacy by arguing that Kennedy would help Trump defeat Biden.

In April, several members of the Kennedy family endorsed Biden, including Kerry Kennedy, sister of the presidential candidate.

“We want to make crystal clear our feelings that the best way forward for America is to reelect Joe Biden and Kamala Harris for four more years,” she said at a campaign event in Philadelphia.

On Wednesday, Kennedy challenged Biden to agree that whichever of them did worse in a head-to-head poll in the fall would drop out of the race to prevent Trump being elected to a second term.

But Republicans including Trump have recently signaled growing concern about Kennedy eating into the former president’s support.

“RFK Jr. is a Democrat ‘Plant,’ a Radical Left Liberal who’s been put in place in order to help Crooked Joe Biden, the Worst President in the History of the United States, get Re-Elected,” Trump posted on Truth Social on April 26, arguing that the candidate opposes gun rights and the military and supports raising taxes, open borders and radical environmental policy. “A Vote for Junior would essentially be a WASTED PROTEST VOTE, that could swing either way, but would only swing against the Democrats if Republicans knew the true story about him.”

Trump posted that before a Monmouth University poll released Monday found that after voters were told about Kennedy’s skepticism of vaccines, their views changed — prior polling showed that Kennedy pulled support evenly from Biden and Trump.

In the new poll, the percentage of Republicans who said they would support Kennedy nearly doubled to almost one out of five after being told about his views about vaccines, while Democrats’ support dropped sharply to roughly 10%.

Kennedy has also been receiving attention on conservative media, such as Wednesday evening on “Jesse Watters Primetime” on Fox News Channel, where he argued that his campaign’s polling shows him winning in a head-to-head matchup against either Biden or Trump.

But “if I’m in the race, in a three-way race, I lose because people are voting out of fear, because they think the other guy — a vote for me is going to put somebody they hate in office,” he said. “But if I go head to head with either of them, I win.”

Trump’s advisors are piqued by Kennedy receiving attention from such outlets.

“For the life of me, I can’t understand why anyone on a conservative platform would feature the likes of Robert F. Kennedy Jr., who believes the NRA is a terrorist organization, whose positions on the environment are more radical than [Rep. Alexandria Ocasio-Cortez], and who believes in a 70% tax bracket,” said Chris LaCivita, a lead strategist for Trump’s campaign and the Republican National Committee’s chief of staff.

“From our standpoint, only one person is more liberal than Joe Biden and that’s Robert F. Kennedy Jr.,” LaCivita said, adding that Kennedy “is a blank canvas and we are going to fill it with paint.”