Several Kennedys - including Robert F. Kennedy Jr.'s siblings - are expected to endorse President Joe Biden's reelection campaign, on Thursday, in a show of unity against their relative's longshot attempt at a third-party challenge in the 2024 presidential race. 

At least 15 members of the United States' most prominent political family are scheduled to appear at a Biden campaign rally in the president's home state of Pennsylvania. Kennedy Jr.'s siblings Joseph, Kerry, Rory, Kathleen, Maxwell and Christopher will appear with Biden.

Kennedy Jr. acknowledged the planned appearances in a statement on X, the platform formerly known as Twitter.

"I hear some of my family will be endorsing President Biden today," he wrote. "I am pleased they are politically active - it's a family tradition. We are divided in our opinions but united in our love for each other."

Kennedy Jr. has previously drawn the ire of his family members - including Jack Schlossberg, the only grandson of President John F. Kennedy.

"[Biden] ended the COVID pandemic and he ended Donald Trump. These are the issues that matter. And if my cousin, Bobby Kennedy Jr., cared about any of them, he would support Joe Biden," Schlossberg said last summer.

"Instead, he's trading in on Camelot, celebrity conspiracy theories and conflict for personal gain and fame."

Kennedy Jr. has a long history of promoting scientifically inaccurate information about vaccines. He has repeated the disproven claim that vaccines cause autism and is one of the most prominent voices in the anti-COVID-19 vaccine movement.

Kennedy cousin and former mayor of Santa Monica Bobby Shriver criticized Kennedy Jr., after his Super Bowl campaign ad used images of Shriver's mother, Eunice Kennedy.

"She would be appalled by his deadly health care views," Shriver wrote on X.

Kennedy Jr.'s younger sister, Kerry, will give remarks at the rally connecting her father's legacy to Biden's political career, political insiders shared.

"I can only imagine how Donald Trump's outrageous lies and behavior would have horrified my father, Robert F. Kennedy, who proudly served as attorney general of the United States, and honored his pledge to uphold the law and protect the country," she is expected to say, according to the New York Times. 

"Daddy stood for equal justice, human rights and freedom from want and fear. Just as President Biden does today."