R.F.K. Jr. Raises New Uncertainty for Biden in Michigan

The prospect of Robert F. Kennedy Jr. threatening to upend the presidential race went from an idea to a reality in one of the country’s most consequential battlegrounds on Thursday, when Mr. Kennedy qualified for the ballot in Michigan.

The decision by the Natural Law Party to grant Mr. Kennedy its ballot line in November ensures he will be a factor in a pivotal swing state where the presidential election is expected to be incredibly close and where President Biden has already shown vulnerability with key Democratic constituencies. During Michigan’s primary in February, a protest movement over Mr. Biden’s support for Israel’s war in Gaza drew significant support.

Mr. Kennedy, a lifelong Democrat and the scion of perhaps the nation’s most famous Democratic family, is running as an independent in 2024 and polling higher in early surveys than any third-party candidate since Ross Perot, the self-funding billionaire who ran in the 1990s.

His independent candidacy has earned him the estrangement of his own family — who campaigned this week with Mr. Biden in Pennsylvania — and many of his previous colleagues from the environmental movement, who denounced his candidacy publicly on Friday.

Mr. Kennedy has emerged as a leading voice of vaccine skepticism, both before and after Covid-19 vaccine, and dabbled in conspiratorial theories, including about the assassination of Robert F. Kennedy, his father. He had initially declared his 2024 campaign as a Democratic challenger to Mr. Biden — and was heavily featured in conservative media — until he switched last fall to run as an independent.

Both parties are already rushing to define Mr. Kennedy as he races to get on the ballot nationwide.

Lis Smith, a Democratic strategist working with the Democratic National Committee, said the Democrats were working to ensure voters “know about how extreme his stances are and that he was recruited to run by Trump allies and funded by Trump’s largest donor to be a spoiler for Trump in November.” Timothy Mellon, the reclusive banking heir, has given $15 million to a pro-Trump super PAC and $20 million to a pro-Kennedy super PAC.