A cousin of Robert F. Kennedy Jr., Bobby Shriver, noted that the ad included images of his mother, Eunice Kennedy Shriver, a sister of both the candidate’s father and the president, both of whom were assassinated. “She would be appalled by his deadly health care views,” Mr. Shriver wrote on X. “Respect for science, vaccines, & health care equity were in her DNA.”

Mr. Kennedy apologized on X “if the Super Bowl advertisement caused anyone in my family pain.” He asserted that the ad had been created by an independent political action committee supporting his campaign without his involvement or his campaign’s approval. Even so, he pinned a link to the ad at the top of his X feed, which has 2.7 million followers.

No matter how much the ad has riled up people in the Kennedy world, the actual political impact of the ad, which cost $7 million to run during the Super Bowl, is far from clear. “The Kennedys have long since passed into history, legend, lore and mythology,” said Evan Thomas, a historian and biographer of Mr. Kennedy’s father. “People barely remember World War II or the Vietnam War. One of the reasons for my double take is, I was put off by it, but also that most people are barely old enough to remember.”

That said, Mr. Kennedy has scored in the double-digits in many polls, owing in no small part to name recognition, political analysts said. And Mr. Kennedy would certainly benefit with being seen as the latest member of this family of Democrats looking to serve the nation.

Bill Carrick, a Democratic consultant and one-time adviser to Edward M. Kennedy, the former senator, said that the new advertisement, which he called distasteful, was particularly hurtful because the original had become part of Kennedy lore. It represented a turning point in how political advertisements were made.