Here’s a question Caroline Kennedy should be able to answer: Why do you want to be the next senator from New York? But, as some have pointed out in recent days, it’s the one question she’s having the most trouble answering, and it could spell the end of her Senate hopes.

"It's really the biggest hurdle she has yet to overcome," says one New York Democratic insider. "To a large degree it's responsible for the lukewarm reception she's been getting."

Lukewarm may actually understate it a bit. Her initial roll-out wasn't a good one, and it was complicated by intra-party squabbles and questions from some New York Democrats about where Kennedy's loyalties really lie.

Once Kennedy realized that the press and the rest of the New York political establishment wasn't going to let her get away with the minimal level of scrutiny she might have hoped for, she went on a media tour. Now, some 300 'you knows' later, Kennedy's political star appears to be fading fast.

A new poll out Monday shows a steep decline in Kennedy's favorability ratings. The new numbers from Public Policy Polling show a full 44 percent of New Yorkers have a less favorable opinion of Kennedy now than they did before she began her "campaign" to fill Hillary Clinton's U.S. Senate seat.

Perhaps her biggest problem over the last month: her seeming inability to answer the “why” question, and to convince New Yorkers that she is really committed to serving in the senate.

You would think it’s the one question Kennedy would be most equipped to answer—and answer well. It was the one that infamously stumped her uncle, Massachusetts Sen. Ted Kennedy, in a 1979 television interview with CBS’ Roger Mudd. When asked, “Senator, why do you want to be president?” Ted Kennedy’s lack of a clear and concise answer made headlines and cost him in the polls.

Caroline Kennedy has been just as vague when probed about her reasons for stepping into the political spotlight. Take this exchange between Kennedy and New York Times reporter David Halbfinger…

Halbfinger: …we’re just trying to establish how much you want this job. You’ve said you want it, you’ve said you think you’d be the best, but again, why would you say that you’d support whoever the governor chooses, and not run, in two years, if you’re not chosen? It just sort of — we were thinking about the way that sounds, and it sounds like you only want it if it’s handed to you.

Kennedy: OK. Well, as I said, I’m interested in this opportunity, this is a complicated process, you know. I am a loyal Democrat, and I believe in the Democratic Party, and I think that we need a team effort here to solve the problems that we have. So I will work with other Democrats, I will continue to advocate for the issues that I believe in, in two years, and I’m making that commitment, and after that, we’ll see what happens. (Pause) That’s a long time from now.

That’s about as non-committal as it gets, and it doesn’t come close to answering that fundamental question.

In the opening pages of her political handbook "Campaign Boot Camp," Christine Pelosi offers this advice to any would-be candidate: "In assessing your own participation in our democracy, the first essential question is, what is your personal call to service?"

If you're running for something, you better know why you're doing it, and you'd better be able to articulate it to a potentially skeptical, if not outright hostile, audience. New Yorkers are known for their skepticism.

Shane D’Aprile is senior editor at Politics magazine.