Caroline Kennedy repeats 'you know' 142 times in interview and won't answer the questions
When she first made it known that she wanted to be appointed to take over Mrs Clinton's seat, Miss Kennedy, 51, the daughter of the assassinated President John F. Kennedy, seemed a near certainty for the job.
But in the course of a few weeks she has alienated Governor David Paterson of New York, who has the sole power to make the appointment, and the American press, including the elite New York Times, which is a powerful influence on Democratic officials.
During an interview with the paper she stumbled badly, fuelling comparisons to Governor Sarah Palin of Alaska, whose bid for the vice-presidency was blighted by a series of disastrous interviews with Katie Couric of CBS News.
Perhaps most damaging of all was her repeated use of the phrase "you know", which she uttered 142 times and was left in the transcript when it appeared in print.
Explaining why she would be a good Senator, she said: "So I think in many ways, you know, we want to have all kinds of different voices, you know, representing us, and I think what I bring to it is, you know, my experience as a mother, as a woman, as a lawyer, you know, I've been an education activist for the last six years here, and, you know, I've written seven books – two on the Constitution, two on American politics.
"So obviously, you know, we have different strengths and weaknesses."
Now Miss Kennedy, who has never held an elected office and often neglected even to vote, is in danger of emulating her cousin Kathleen Kennedy Townsend, daughter of Robert Kennedy, who was shot dead in 1968 while he was a Senator for New York.
An uncomfortable campaigner, Mrs Kennedy Townsend, then lieutenant governor of Maryland, ran for governor of the heavily-Democratic state in 2002 but slumped to an ignominious defeat.
Miss Kennedy, who had always shunned the limelight before her high-profile endorsement of Barack Obama for president in February, also appears to be a reluctant politician.
Her uncle Senator Ted Kennedy of Massachusetts, who is stricken with brain cancer, is understood to have played the crucial role in persuading his niece to seek the seat, which would ensure the Kennedy legacy continues in the Senate.
The full transcript of the New York Times interview, revealed a series of tetchy exchanges.
At one point Miss Kennedy, being asked to describe the moment she decided she wanted the Senate seat, asked the reporters: "Have you guys ever thought about writing for, like, a woman's magazine or something?" One of them responded: "What do you have against women's magazines?" Miss Kennedy shot back: "Nothing at all, but I thought you were the crack political team here."
Another reporter asked "Would you have sought this if there hadn't been an appointment open, if it had been an election?", Miss Kennedy said: "I think we covered that." The reporter pressed: "What's the answer, then, if we covered it?" When Miss Kennedy was asked in what ways she would be a better Senator than Mrs Clinton, she responded that "when I get in there, then I can really tell you exactly how I would improve on it".
She refused to say anything about her wealth and declined to take policy stances even on hot-button issues in education, her specialty.
Asked about performance pay for teachers, she said only that "it'll be really interesting to see what happens. There's a lot of experimentation going on in the country that we should pay attention to".
Michael Goodwin, a New York Daily News columnist urged her to "Say goodnight, Caroline", arguing she had "flubbed" the audition to become the next Senator Kennedy.
The "wheels of the bandwagon are coming off" and "fantasy is giving way to inescapable truth", he wrote. "That truth is that Kennedy is not ready for the job and doesn't deserve it. Somebody who loves her should tell her. Her quest is becoming a cringe-inducing experience, as painful to watch as it must be to endure."