In 1974, the independent California Poll showed him to be more popular than Mr. Reagan, then in his last year as governor. In 1975, Mr. Tunney led a successful fight in the Senate to cut off funds for covert military operations by pro-American rebels in Angola. Mr. Tunney and like-minded lawmakers feared that involvement in Angola could lead to a Vietnam-like quagmire in Africa.

But many liberal Democrats were disenchanted with him. They thought he had been too slow to turn against the Vietnam War, which he had supported early on, and they were disappointed by his refusal to embrace a boycott of California grapes by striking farm workers.

Liberals found a champion in Tom Hayden, the former campus radical, who challenged Mr. Tunney in the 1976 Senate Democratic primary. Mr. Hayden raised a lot of money and was a surprisingly effective campaigner, accusing Mr. Tunney of being beholden to big business, though Mr. Tunney had supported antitrust legislation as a senator.

Mr. Hayden also sought to turn Mr. Tunney’s friendship with Senator Edward M. Kennedy against him, calling Mr. Tunney “a Chappaquiddick waiting to happen,” a reference to the 1969 incident in which the political aide Mary Jo Kopechne died when the car in which she was riding, driven by Mr. Kennedy, plunged off a bridge on Chappaquiddick Island in Massachusetts.

Mr. Hayden later apologized for the remark. But after finishing a strong second in the June primary, Mr. Hayden offered only the most tepid support for Mr. Tunney in the general election. And the Kennedy allusion, fair or not, fanned complaints that Mr. Tunney preferred the companionship of elite Easterners over the company of Californians.

In fact, Mr. Tunney was a transplanted Californian, having had a privileged childhood in the East. His father, the former heavyweight boxing champion Gene Tunney, read widely and aspired to social status to go with his ring riches. He achieved it in 1928, when he married Polly Lauder, an heiress to the Carnegie steel fortune.

John Varick Tunney was born on June 26, 1934, in New York City. He grew up in Connecticut with his brothers, Jay and Gene, who is deceased, and a sister, Joan, who is also deceased. He studied anthropology at Yale, graduating in 1956. He attended the Hague Academy of International Law, worked on John F. Kennedy’s 1958 Senate campaign in Massachusetts and roomed with Edward Kennedy at the University of Virginia Law School, graduating in 1959.