The presidential bid by Robert F. Kennedy Jr. has tested the bonds of an iconic Democratic clan that does not want him to run and does not know what to do about it.Jack Schlossberg had enough. The only grandson of President John F. Kennedy, Mr. Schlossberg had been watching the presidential campaign of his cousin Robert F. Kennedy Jr. with increasing dismay.To Mr. Schlossberg, the quixotic challenge to President Biden for the Democratic nomination was just a “vanity project” that was tarnishing the legacy of his grandfather and their storied family. Just days earlier last month, his conspiracy-minded cousin had suggested that the Covid-19 virus had been engineered to protect Ashkenazi Jews and Chinese people.Sitting in a van in Australia, where he was on vacation, Mr. Schlossberg sketched out a few bullet points, took out his mobile phone and recorded a harsh condemnation of his cousin on Instagram. “He’s trading in on Camelot, celebrity, conspiracy theories and conflict for personal gain and fame,” Mr. Schlossberg said. “I’ve listened to him. I know him. I have no idea why anyone thinks he should be president. What I do know is his candidacy is an embarrassment.” Then he hit the post button.Mr. Schlossberg’s denunciation underscored the turmoil inside what remains of Camelot. Bobby, as the 69-year-old candidate is called, has become a source of deep anguish among his many siblings, cousins, nieces and nephews, one that is testing the bonds of what was once known as the royal family of American politics. His relatives by and large do not want him to run, do not support his campaign, disdain his conspiratorial musings and almost universally admire Mr. Biden, a longtime friend of the family who keeps a bust of Robert F. Kennedy Sr. in the Oval Office.President Joe Biden keeps a bust of Robert F. Kennedy Sr. on display in the Oval Office. Pool photo by Al DragoYet even as some members of the candidate’s family feel compelled to speak out against his campaign, others find themselves profoundly pained by the airing of domestic discord. They do not share Bobby’s views on many issues, particularly his strident anti-vaccine stances, these Kennedys say, but they care for him, do not want to see him hurt and do not think it helps to publicly criticize him.“I love my brother deeply, and while I don’t agree with him on a number of issues, theories, I do not want to knock him,” said Courtney Kennedy Hill, one of the candidate’s sisters. “He has done a lot of good for many, many people,” she added, citing his work as an environmental lawyer who helped clean up the Hudson River and his advocacy for those struggling with drug addiction. “I just don’t want all that to get lost in the maelstrom around his more controversial statements and views.”Robert F. Kennedy Jr., known as Bobby, in the middle row on the right, appears in a portrait with his family in 1964.Bettmann Archive/Getty ImagesNever before has the family faced a conundrum quite like this. Through all the tragedies and scandals and campaigns over the years, the traditional Kennedy rule has always been to pull together, to stand by one another no matter what. Family was the rock. Solidarity was the code. But as he polls at around 15 percent against Mr. Biden, Bobby has roiled a family that wants nothing to do with his campaign and telephone lines between Kennedy homes burn with what-to-do agonizing.At left, John F. Kennedy, and in the foreground, Edward M. Kennedy, known as Ted. In a family once considered American royalty, marked by political ambitions and public tragedy, solidarity was long the code.Kennedy Family Collection, Courtesy of the John F. Kennedy Library Foundation, via Associated Press“It must be painful for them,” said Bob Shrum, who for years was one of the leading advisers to Edward M. Kennedy, the senator and patriarch known as Ted. “He’s been through some struggles himself,” Mr. Shrum added of Bobby, “and I think they want to love him. But at the same time, they can’t abide this. It’s very sad at every level.”Robert Kennedy Jr. opted against discussing his relations with his family. “It’s pretty clear that the Times is not going to treat me fairly honestly so I’m going to decline,” he said in a text message. In a statement to CNN in April shortly before kicking off his campaign, he acknowledged that some relatives do not support him. “I bear them no ill will,” he said. “Families can disagree and still love each other.”Still, privately he has reached out to some of his relatives to complain about their public comments and engaged in tense discussions about his campaign and platform. Some family members recall pressing him on why he was running and warning him that he was putting his life up for scrutiny in a way that might be personally devastating.Mr. Kennedy, who was 9 when his uncle was assassinated and 14 when his father was killed, struggled with addiction as a young man and was kicked out of private schools and arrested on marijuana and heroin charges more than once. After checking into a treatment facility in 1983, he says he has been clean ever since and has been an antidrug crusader. Amid reports of infidelity, he separated from his second wife, Mary Richardson Kennedy, who also battled addiction and died by suicide in 2012. He is now married to his third wife, the actress Cheryl Hines.Mr. Kennedy and his wife Cheryl Hines in Israel in 2019 as part of a trip with the Waterkeeper Alliance, of which he was board president in his environmental advocacy.Daniel Rolider for The New York TimesIn interviews in recent days, several members of the Kennedy family, some of whom did not want to be named, sounded tortured about the situation. They talked of a brother, cousin, uncle who flashed some of the raw political talent of his famed father, but who has undergone trauma and is headed down a path they do not fully understand.For years, Mr. Kennedy has made himself into a champion of the vaccine resistance movement, promoting spurious assertions about the dangers of inoculations and once calling the Covid-19 vaccine the “deadliest vaccine ever made.” He has said Anne Frank had more freedom during the Holocaust than Americans pressured to take the vaccine, a comparison for which he later apologized, and wrote a book attacking Dr. Anthony S. Fauci.He has suggested that mass shootings at schools have increased because of heightened use of antidepressants. And in a particularly sensitive area for his family, he has maintained that the C.I.A. was involved in the assassination of his uncle, John F. Kennedy, and possibly in the assassination of his father.Last month, he declared that the coronavirus was “targeted to attack Caucasians and Black people” and that “the people who are most immune are Ashkenazi Jews and Chinese.” He later said he was misinterpreted, writing on Twitter that the disparate effect of the virus “serves as a kind of proof of concept for ethnically targeted bioweapons” but “I do not believe and never implied that the ethnic effect was deliberately engineered.”That proved too much for several family members. Kerry Kennedy, his sister and president of Robert F. Kennedy Human Rights, issued a statement calling his remarks “deplorable and untruthful.” Joseph P. Kennedy II, his brother and a former congressman, called them “morally and factually wrong.” Joseph P. Kennedy III, his nephew and another former congressman now serving as Mr. Biden’s special envoy to Northern Ireland, posted his own response on Twitter: “I unequivocally condemn what he said.”Mr. Kennedy protesting a Covid-19 vaccine mandate in Washington in January 2022. Last month, he declared that the coronavirus was “targeted to attack Caucasians and Black people.”Victor J. Blue for The New York TimesMr. Schlossberg filmed his video four days later. “I didn’t have a plan,” he said in an interview from Australia, where he traveled after passing the bar exam to visit his mother, Caroline Kennedy, the U.S. ambassador, and to tour the country before returning home to begin a legal career. “I just wanted to speak out and felt it was the right time.”Mr. Schlossberg, 30, said he did not consult family members first and added that posting the video was “not an easy thing to do.” But he stressed how much he admires Mr. Biden, who he said “sees America now much the same way as my grandfather did” and in his view is “probably the greatest president of my lifetime.”While the statements were not coordinated, according to family members, the display of disagreement struck close observers of the Kennedys as a pivotal moment. “The Kennedy family has always tried to keep things within the family,” said Jim Manley, a longtime aide to Edward Kennedy. “The fact that some of the members, some of his cousins, are beginning to speak up publicly, it to me indicates how upset they are with what he’s saying and what he’s doing.”Vaccines are not the only source of dispute. The candidate has also spoken out against aid for Ukraine, accused the Biden administration of lying to the public about the war and suggested that American leaders pushed Ukraine into conflict with Russia “as part of their strategic grand plan to destroy any country such as Russia that resists American imperial expansion.”“I do not agree with Bobby on Ukraine, and I’ve had many conversations with him about it and I’m disappointed that he is not more supportive,” Douglas Kennedy, another brother and a Fox News correspondent, said in an interview.Still, he expressed understanding for his brother’s propensity to question conventional wisdom. “Bobby has views that I would say most of the members of my family disagree with,” he said. “But I also believe that particularly our family, our siblings, we were brought up to be skeptical of authority in general.”Mr. Kennedy appeared at a House Judiciary Committee hearing last month organized by Republicans, on the weaponization of the federal government.Kenny Holston/The New York TimesPatrick J. Kennedy, another former congressman and son of Edward Kennedy, said he regrets that the campaign has distracted from priorities the family has long promoted. “It would be nice for the general public who is associating the legacy of my family with my cousin (esp bc he invokes them so much) to know that my family’s historic legacy of fighting for social justice was on display today,” he said by text on the day the Biden administration advanced new rules aimed at increasing access to mental health and substance abuse services.It has not been lost on the family that Robert Kennedy Jr. has drawn support from Republicans affiliated with former President Donald J. Trump. Roughly half of the $10.5 million raised by two super PACs supporting Mr. Kennedy came from a single donor who previously backed Mr. Trump and has contributed $53 million in stock to build a wall on the border with Mexico.Nor is Mr. Kennedy’s target immaterial. Mr. Biden has been close to the Kennedys for half a century, since the days when Edward Kennedy showed up at the Delaware hospital where his sons were recovering from the car accident that killed the future president’s first wife and baby daughter.To this day, Mr. Biden calls the candidate’s mother, Ethel Kennedy, every year on her birthday and for decades, according to Douglas Kennedy, has shown up for family events two or three times a year. The president has dispensed appointments to multiple members of the family, including Victoria Reggie Kennedy, the ambassador to Austria; Kathleen Kennedy Townsend, a senior Labor Department official; Caroline Kennedy and Joseph Kennedy III.Joseph R. Biden Jr. and Edward M. Kennedy during a Senate hearing with Attorney General Edwin Meese in 1987. The ties between the Biden and Kennedy families go back to the 1970s.Jose R. Lopez/The New York Times“Everybody in our family loves Joe Biden, and Joe Biden has been very good to my mother and I think genuinely loved my father probably as much as anybody who has held that office in the past 50 years,” Douglas Kennedy said. “That’s certainly a factor in everybody’s individual feeling about Bobby running.”Courtney Kennedy Hill recalled how “exceptionally kind, thoughtful and valuable” Mr. Biden was when her daughter, Saoirse Kennedy Hill, died of an overdose in 2019. But so too was Bobby, she noted. He had a close relationship with his niece. “He was special to and for her and I will love him forever for that,” she said.One way or the other, she predicted, the family would get through this. “If you came to the Cape on Thanksgiving, you would see a family full of fun, energy, laughter and, of course, healthy competition,” she said. “A lot of it anyway.” More