Those ideas on home schooling and home birth later became more popular. Some of his other ideas have yet to catch on.

In December 1969, he published in The Freeman “Cancer, Disease and Society,” an article based on the work of the Austrian psychologist Wilhelm Reich, exploring whether sexual repression and the stifling of children contributed to cancer.

The “manner in which you bring up your daughter with regard to sexual attitudes may very well determine whether or not she will develop breast cancer, among other things,” he wrote. He added that it was important for boys to rebel in school because if they bottled up their emotions, “30 years later, a doctor tells him that he has cancer.”

Mr. Sanders also thought children should be allowed to vote once they reached puberty. A political ally, Peter Diamondstone, who thought the voting age should be abolished altogether, recalled asking Mr. Sanders: “So every time you want to have a kid vote they have to go get a physical?”

But when it came to his own son, Mr. Sanders was more traditional.

Mr. Sanders gave clear boundaries to Levi, with whom he could occasionally be “overbearing,” according to Nancy Barnett, a friend. She recalled one day when Mr. Sanders, a former cross-country star, ran laps with Levi around the high school track until the 9-year-old stopped with exhaustion.

“Bernie was adamant,” she recalled. “‘You started your race — now you’ve got to finish your race.’”

Mr. Sanders, as his campaigning has shown, is nothing if not perseverant.

His outsider campaigns for governor and senator, conducted much of the time with Levi in tow, went nowhere. With Ms. Barnett, he scraped together a living selling very low-budget films, sometimes using Levi’s toy robot for sound effects, about historical figures like Ethan Allen and Eugene V. Debs. He wrote freelance articles, put down flooring and, for a time, collected unemployment. After his rent skyrocketed, he crashed in 1979 at the home of a good friend, Richard Sugarman, who had once been former Senator Joseph I. Lieberman’s suite mate at Yale.