Longtime environmental lawyer and anti-vaccine activist Robert F. Kennedy Jr. said Monday he will run for president as an independent and drop his Democratic primary bid, likely pitting him against President Joe Biden, who is running for reelection, and the winner of the Republican nomination. Former President Donald Trump is currently leading national and early-contest polls in the GOP race.

Kennedy's campaign teased the announcement in the days leading up to his Monday afternoon speech in Philadelphia. In a recent video, Kennedy said there is corruption "in the leadership of both political parties" and said he wants to "rewrite the assumptions and change the habits of American politics."

A member of one of America's most famous Democratic families, the 69-year-old Kennedy was running a long-shot Democratic primary bid but has better favorability ratings among Republicans. It's unclear whether GOP support would translate to a general election when Kennedy would also be running against Trump, the early front-runner for the GOP presidential nomination. Allies of both Biden, a Democrat, and Trump have at times questioned whether Kennedy would be a spoiler against their candidate.

But four of Kennedy's siblings, documentary filmmaker Rory Kennedy, human rights activist Kerry Kennedy, former Rep. Joe Kennedy II and former Maryland Lieutenant Gov. Kathleen Kennedy Townsend immediately condemned his decision to run against Mr. Biden as "dangerous to our country."

"Bobby might share the same name as our father, but he does not share the same values, vision or judgment. Today's announcement is deeply saddening for us," they said in a statement. "We denounce his candidacy and believe it to be perilous for our country."

Biden's allies so far have dismissed Kennedy's primary campaign as unserious. Asked for comment on his potential independent run, a Democratic National Committee spokesman responded with an eye roll emoji.

Maryland voter Andrea Levinson, who describes herself as a lifelong liberal Democrat and says she supported Mr. Biden in the past, attended Kennedy's announcement. She was thrilled to hear Kennedy announce his independent bid.

"I am so I'm so excited because they can't ignore him…the DNC can't put him down," Levinson told CBS News. She said her discontent regarding the Democratic Party and the narrative that voting for Mr. Biden is the way to get rid of Trump drove her to change her view.

"So, now as Kennedy gets out…I think people may listen because they don't want Biden, they don't want Trump, they're worried that he's a spoiler," said Levinson.

Monday's announcement comes less than a week after the progressive activist Cornel West abandoned his Green Party bid in favor of an independent White House run. Meanwhile, the centrist group No Labels is actively securing ballot access for a yet-to-be-named candidate.

Kennedy has spent weeks accusing the DNC of "rigging" the party's primary against him and threatening that he might need to consider alternatives.

In campaign emails and videos, he blasted the DNC's decision not to host debates between Biden and other candidates and railed against the committee's plan to give South Carolina rather than Iowa or New Hampshire the leadoff spot on the primary calendar this election cycle.

"If they jam me, I'm going to look at every option," he said in September at a New Hampshire barbecue held by Republican former Sen. Scott Brown.

Far-right and anti-vaccine influencers close to Kennedy also have sent strong signals on social media suggesting he should or will leave the Democratic Party. Last month, Joseph Mercola, an influential anti-vaccine doctor who is allied with Kennedy, ran a poll on X, formerly known as Twitter, asking if Kennedy should quit the party.

While Kennedy has long identified as a Democrat and frequently invokes his late father, Sen. Robert F. Kennedy, and his uncle President John F. Kennedy on the campaign trail, he has built close relationships with far-right figures in recent years. He appeared on a channel run by the Sandy Hook conspiracy theorist Alex Jones and headlined a stop on the ReAwaken America Tour, the Christian nationalist road show put together by Trump's former national security adviser Michael Flynn.

Polls show far more Republicans than Democrats have a favorable opinion of Kennedy. He also has gained support from some far-right conservatives for his fringe views, including his vocal distrust of COVID-19 vaccines, which studies have shown are safe and effective against severe disease and death.

Kennedy's anti-vaccine organization, Children's Health Defense, currently has a lawsuit pending against a number of news organizations, among them The Associated Press, accusing them of violating antitrust laws by taking action to identify misinformation, including about COVID-19 and COVID-19 vaccines. Kennedy took leave from the group when he announced his run for president but is listed as one of its attorneys in the lawsuit.

Cristina Corujo and Kathryn Farrell contributed to this report.

In:
• Joe Biden
• Donald Trump
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• Robert F. Kennedy Jr.
• Philadelphia