Starting in 1989, when the Keating scandal broke, and leading into her husband's 1992 reelection campaign, she was taking painkillers initially prescribed for her after back surgery. Soon she was stealing pills from the relief organization, doubling the amount the group needed and keeping a supply for herself.
The Drug Enforcement Administration began a probe into the group's records -- sending agents to Mrs. McCain's home and asking about the missing pills after hearing of the problems from aformer co-worker.
Too mortified to tell her husband, she had his Washington lawyer call him with the news. McCain said he never suspected she was battling an addiction.
"I called her, and she cried and cried," recalls brother-in-law Joe McCain. "It was the kind of cry [that] when you hear it, you would just do anything to stop it and you can't. It's the only time I've ever seen her really vulnerable."
Although long wary of the press, she handpicked five reporters and gave them her side of the story. But the McCains could not control the fallout as the news unfolded. John McCain refused to speak to the Arizona Republic for at least a year after it ran an editorial cartoon of Mrs. McCain literally shaking down a child for drugs while on a relief mission.
Mrs. McCain quit the drugs cold turkey in 1992, when she avoided criminal charges by cooperating with the U.S. Attorney and agreeing to community service. She still attends a drug-addiction support group and says she will always be "in recovery." She continues to relive the episode on the trail, patiently working through the details in each new city.
She is far more comfortable on other subjects, such as her daughter, Bridget, whose story was retold in early campaign commercials. Eight years ago in Mother Teresa's orphanage in Bangladesh, Mrs. McCain was asked to bring Bridget to the United States to treat a severely cleft palate. By the time the plane landed, she says, she could not part with the infant.
The campaign has claimed that McCain critics have used the interracial adoption as fodder for racially charged phone calls against McCain. The campaign of Republican rival George W. Bush denies any association with that activity. Mrs. McCain says she has swung from tears to rage over the phone calls and has not told her daughter about them.
To some friends, the later years have brought out a Cindy McCain they never knew.
"Trust me, Cindy Hensley was not on any social welfare crusade in college," says Tracy Hayward Osuch, a sorority sister and friend from the University of Southern California. "This woman adopted a child of another color; that's a big stretch. Most people don't bend the envelope like that in their lives -- they don't go beyond the parameters of their upbringing. She's reached out beyond that."
To others, it seemed perfectly in character. Before she met John, as a special-education teacher in a Phoenix neighborhood of migrant workers, Mrs. McCain broke school rules and paid house calls to students. Later, she took in the teen-age daughter of a cousin and called her a child of her own. Today, from the frenzy of the campaign, she calls her relief work "a part of me that is still very much alive."
But it is her husband's ambitions that dominate her life now. Almost despite herself, she is swept up in the McCain crusade. "I completely and fully expected to hate every minute of it," she says. "But I walk into a crowded hall and hear everyone cheering for my husband. How can you not love that?"