Kennedy Clan to Endorse Biden, in a Show of Force Against R.F.K. Jr.

A broad coalition of the Kennedy family will endorse President Biden on Thursday at a campaign rally in Philadelphia, pointedly rejecting one of their own in Robert F. Kennedy Jr., the independent candidate who many Democrats believe poses a significant threat to Mr. Biden’s re-election chances.

Among the relatives of Mr. Kennedy expected to back Mr. Biden are his siblings Joseph, Kerry, Rory, Kathleen, Maxwell and Christopher. The Biden campaign released a list of 15 Kennedys set to appear at the rally, but it said other family members would endorse the president as well. Kerry Kennedy will introduce Mr. Biden at the rally, the campaign said, and Joe Kennedy III, Mr. Kennedy’s nephew and a former Democratic congressman from Massachusetts, will do so at a second event.

The show of force will send the clearest signal yet that America’s most storied Democratic family is deeply fearful that one of its own could tip the 2024 election to former President Donald J. Trump, and hopes to use its influence to try to stop him.

Many family members have previously expressed strong disapproval of Mr. Kennedy’s candidacy, voicing anguish about his promotion of conspiracy theories and confusion about why he is challenging a Democratic president they admire. Like many Democrats, they worry that he could help Mr. Trump win if he draws even a small number of votes away from Mr. Biden in the battleground states — contests that were decided by tens of thousands of votes in 2020.

Mr. Trump is likely to remain the main target of attacks at the Philadelphia event, but the symbolic repudiation of Mr. Kennedy will not be subtle.

“We can say today, with no less urgency, that our rights and freedoms are once again in peril,” Kerry Kennedy is expected to say, according to excerpts from her speech shared by the Biden campaign. “That is why we all need to come together in a campaign that should unite not only Democrats, but all Americans, including Republicans, and independents, who believe in what Lincoln called the better angels of our nature.”