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Mr. McCain’s confidence in his ability to distinguish personal friendships from compromising connections was at the center of questions advisers raised about Ms. Iseman.

The lobbyist, a partner at the firm Alcalde & Fay, represented telecommunications companies for whom Mr. McCain’s commerce committee was pivotal. Her clients contributed tens of thousands of dollars to his campaigns.

Mr. Black said Mr. McCain and Ms. Iseman were friends and nothing more. But in 1999 she began showing up so frequently in his offices and at campaign events that staff members took notice. One recalled asking, “Why is she always around?”

That February, Mr. McCain and Ms. Iseman attended a small fund-raising dinner with several clients at the Miami-area home of a cruise-line executive and then flew back to Washington along with a campaign aide on the corporate jet of one of her clients, Paxson Communications. By then, according to two former McCain associates, some of the senator’s advisers had grown so concerned that the relationship had become romantic that they took steps to intervene.

A former campaign adviser described being instructed to keep Ms. Iseman away from the senator at public events, while a Senate aide recalled plans to limit Ms. Iseman’s access to his offices.

In interviews, the two former associates said they joined in a series of confrontations with Mr. McCain, warning him that he was risking his campaign and career. Both said Mr. McCain acknowledged behaving inappropriately and pledged to keep his distance from Ms. Iseman. The two associates, who said they had become disillusioned with the senator, spoke independently of each other and provided details that were corroborated by others.

Separately, a top McCain aide met with Ms. Iseman at Union Station in Washington to ask her to stay away from the senator. John Weaver, a former top strategist and now an informal campaign adviser, said in an e-mail message that he arranged the meeting after “a discussion among the campaign leadership” about her.

“Our political messaging during that time period centered around taking on the special interests and placing the nation’s interests before either personal or special interest,” Mr. Weaver continued. “Ms. Iseman’s involvement in the campaign, it was felt by us, could undermine that effort.”

Mr. Weaver added that the brief conversation was only about “her conduct and what she allegedly had told people, which made its way back to us.” He declined to elaborate.

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