Antivaccine activist Robert F. Kennedy Jr. filed paperwork Wednesday to run for president as a Democrat in a long-shot bid against President Biden.
 Mr. Kennedy, son of former Attorney General Robert F. Kennedy and nephew of former President John F. Kennedy, declared his candidacy by filing a statement with the Federal Election Commission. He joins self-help author and activist Marianne Williamson in a 2024 Democratic field that is unlikely to include any major challengers to Mr. Biden.
 Mr. Kennedy will officially announce his candidacy at an April 19 event in Boston, his campaign said.
 Mr. Kennedy, 69 years old, is a former environmental lawyer who has spent more than a decade pushing antivaccine conspiracy theories. He led a campaign casting doubt on Covid-19 vaccines and in 2021 saw his account removed by Instagram as part of Facebook’s and later its parent company Meta Platforms Inc.’s efforts to crack down on false and misleading information about the virus.
 Filings with charity regulators showed his antivaccine group, Children’s Health Defense, more than doubled its revenue to $6.8 million in 2020, the first year of the Covid-19 pandemic. Mr. Kennedy also released a book in 2021, “The Real Anthony Fauci,” in which he accused Mr. Biden’s former chief medical adviser of helping lead “a historic coup d’état against Western democracy.”
 Mr. Kennedy has also pushed claims debunked by public-health experts linking childhood vaccinations to autism. Some members of his family have publicly rejected his views. Kerry Kennedy, Mr. Kennedy’s sister, dubbed his work “completely wrong” and “dangerous” in a 2021 interview.
 Mr. Kennedy said on Twitter in March, “If I run, my top priority will be to end the corrupt merger between state and corporate power that has ruined our economy, shattered the middle class, polluted our landscapes and waters, poisoned our children, and robbed us of our values and freedoms.”