Observers of that campaign and the current one say she seems different this time — more guarded, more tense, superthin. She rarely campaigns away from her husband’s side, and yet their interactions on the trail often appear brief and formal. During the rolling primary-season seminars that Mr. McCain held in the back of his bus, Mrs. McCain sat up front. Once in a while, she joined him, sitting very straight, smiling and saying little. Physically, she seems fragile: she suffers from migraines, hobbled around on crutches last year after a knee injury and recently wore a wrist brace because of a handshaking injury.

In speaking about each other, the McCains use standard lines: she praises his experience, he tells the crowd that she should really be the candidate. Meghan McCain, their daughter, performs the image-softening role spouses usually perform for each other: on her blog, she depicts her father joking around on campaign planes and her mother in polka-dot pajamas. On Friday, Mrs. McCain made rare contact with the reporters covering her husband, distributing Halloween candy and gaily advising, “Make your dentist happy!”

In interviews, some of Mrs. McCain’s statements seem questionable. She often tells of how she moved to California, leaving her children behind, for four months in 2004 to recover from a stroke that left her unable to walk or speak. But news reports from the time indicate she had few discernible impediments. She gave interviews four days afterward, attended a baseball game with her husband and a reporter several weeks later, and spoke at a Tempe, Ariz., Chamber of Commerce event. “One month out, I feel wonderful,” she told the audience. The McCain campaign declined to resolve the discrepancy.

Similarly, Mrs. McCain often mentions her travels to Rwanda at the height of the 1994 genocide — she wrote about it in a recent Wall Street Journal opinion piece and has been praised by politicians and newspaper columnists for jetting into the heart of a massacre. As with her other charity trips, participants praised her eagerness to help victims of tragedy. But news accounts and interviews indicate, and a campaign spokesman confirmed, that Mrs. McCain traveled after the genocide had ended, spending time with refugees in neighboring Zaire, now Congo. Asked if she was ever in Rwanda, as Mrs. McCain has stated many times, a campaign spokesman, Jill Hazelbaker, said “she was driven to the Zaire/Rwanda border in order to assess the conditions of the refugees entering the country.”

Whatever stumbles she may have made in telling her story, Mrs. McCain has exhibited the signal trait of the political spouse: a burning desire to win. In summer 2007, she helped reorganize her husband’s campaign after it almost fell apart, sitting down with the books to review the cash-flow. Rick Davis, a contentious figure in the McCain camp because of his lobbying ties, emerged as campaign manager, in part because Mrs. McCain, with whom he spent months traveling and fund-raising, backed him.

“It was at a time when most people had given up on John,” said Mr. Salmon, the former Arizona congressman. “When he was down, Cindy was extremely positive.”

Asked to explain how Mrs. McCain can seem so uncomfortable on the trail and yet so intent on victory, friends say she truly believes that her husband is the best man for the job. Some note she has invested for decades in his career and now sees the ultimate prize in reach; others say she wants approval, from either her husband or the public. At a Florida rally on Thursday, the crowd greeted her with chants of “Cin-dy! Cin-dy!”

If Mr. McCain wins, she would have to return to the town she says she dislikes, attending the same sorts of luncheons she once fled from. But this time — maybe at the annual event that Congressional wives have for the first lady — the women of Washington, including a few who shunned her the first time around, would have to applaud in Mrs. McCain’s honor.