Waging an underdog campaign for president, Robert F. Kennedy Jr. is hitting the gridiron with a retro commercial echoing from its debut in Super Bowl LVIII. It scores in several ways, impressing upon the nation that the Independent is playing November’s big game to win.

The commercial reused a 1960 campaign song from President Kennedy, Mr. Kennedy’s uncle. The catchy popular march — reminiscent of the Irish-American song, “McNamara’s Band” — is an earworm, and it fit this moment with age at the forefront of voters’ minds.

JFK, at 43 the youngest president ever elected, asked Americans to vote for a new generation of leadership. The term-limited incumbent, 70-year-old President Eisenhower, was the oldest man to serve as president at the time, as President Biden, 81, is today.

“Do you want a man for president who’s seasoned through and through,” the lyrics ask, “a man who is old enough to know and young enough to do?” Mr. Kennedy, 70, is younger than both Mr. Biden and President Trump, 77.

The 1960 ad had one- and two-minute versions. Mr. Kennedy’s trimmed that to 30 seconds, a spot priced at about $7 million. American Values 2024, a super PAC, bought the time. A record 115.1 million people watched last year’s game. Yesterday’s contest is expected to have surpassed that.

Mr. Kennedy’s main asset is his family name. The song hammers it seven times at the top and repeats it four times later. “Kennedy” appears on screen 27 times. The final shot lingers on a campaign button reading, “Kennedy for President 2024,” bearing Mr. Kennedy’s face.

The commercial does its job invoking nostalgia for previous Democratic campaigns. President Kennedy was slain in 1963, as was, during the 1968 primaries, his brother, Senator Robert Kennedy Sr. The last surviving brother, Senator Edward Kennedy, challenged unsuccessfully President Carter for the party’s nomination in 1980.

Many Democrats still revere the Kennedy “Camelot” mystique, but party leaders soured on Mr. Kennedy when he entered this season’s primaries against Mr. Biden. Now, they worry that his run will draw more support from the president, helping Mr. Trump.

A Democratic strategist, Robert Shrum, took to X to call the commercial “straight-out plagiarism,” and invoked the quip by Senator Lloyd Bentsen in his 1988 debate with Vice President Quayle. “Bobby,” Mr. Shrum said, “you’re no John Kennedy. Instead, you are a Trump ally.”

More damaging than the complaints by Mr. Shrum — who worked on eight presidential campaigns, all unsuccessful — might be tweets like the one by Mr. Kennedy’s cousin, Robert Shriver, who objected to the use of “our uncle’s faces” and that of his mother, Eunice Shriver.

Mr. Shriver said his mother “would be appalled” by Mr. Kennedy’s “deadly health care views. Respect for science, vaccines, & health care equity were in her DNA.” His brother, Mark Shriver, tweeted, “I agree.” The schism is reminiscent of the Roosevelt dynasty splitting into factions over President Theodore Roosevelt, a Republican, and President Franklin Roosevelt, a Democrat.

“RFK Jr. is on the outs with almost the entire extended Kennedy Clan,” the author of “Coming to Terms with John F. Kennedy,” Stephen F. Knott, tells the Sun. “They do not see him as an heir to either JFK or RFK.” A professor at the U.S. Naval War College who worked on Senator Edward Kennedy’s campaign in 1976, he said the ad “shocked the hell out of me.”

A Kennedy cousin, Jack Schlossberg, “called RFK Jr.’s campaign ‘an embarrassment’ last fall,” Mr. Knott said. “I have to believe that comment was cleared by his mother,”Caroline Kennedy, who is JFK’s daughter and Mr. Biden’s ambassador to Australia.

“Perhaps his PAC knows something I don’t,” Mr. Knott said. “If they believe they will win some Baby-Boomers yearning for a return to Camelot, I think they’re deluding themselves. Camelot worshippers are not likely to embrace the policy positions of RFK Jr.”

Mr. Kennedy seems untroubled by the criticism. “Our momentum is growing,” he posted on X along with the commercial. “It’s time for an independent president to heal the divide in our country.” Whether or not voters agree, his Super Bowl play has them talking about his candidacy — quite a bang for his super PAC’s buck.