Hillary Clinton has a fundraising pot that is overflowing. She appears to be cruising to the 2016 Democratic presidential nomination: and then, if the stars align in her favour, on to a well-deserved place in history as the first female president of the United States.

Her supporters have wished it for so long, it seems almost impossible that it might not come to pass. And I would count myself among those supporters, ever since – as a Washington-based correspondent – I watched the lobbyists gang up to defeat her health plan, and observed how she toughed out the sordid revelations about her husband and “that woman, Miss Lewinsky”.

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Clinton, as she showed then and has shown since, is not one to walk away. She embodies that all-American quip about the going getting tough and the tough getting going. But I just hope that there are those, somewhere in her entourage, who are even now begging her not to do it, and to bow out while there is still time to do so with grace.

Reality must be looked in the eye. Clinton is a hugely divisive figure, including within her own party – and not primarily because she is a woman. There is the clan question. What does it say about the meritocratic credentials of the United States that two of the most favoured candidates for 2016 are closely related to recent presidents? Neither is to blame but in my book, this alone would be a reason for both Clinton and Jeb Bush to leave the field. It is also a reason why they may not be electable.

Then there is the Bill question. A large section of the Republican party hates the Clinton name with the same venom that many Britons reserve for Margaret Thatcher, blaming Bill, as they see it, for defiling the presidency. This should not affect Hillary Clinton’s support – but it will limit her ability to appeal across parties. Nor do US voters need to be dragged all over again through the intricacies of the (loss-making) Whitewater land deal, the involvement of the Rose Law firm, or the suicide of a close aide, but they probably will. And if these Bill questions are not enough, there is another where she really does have some explaining to do: it concerns her involvement with his post-presidential charitable fundraising at a time when she held public office.

Clinton’s chief liability, though, is the baggage she carries of her own. This includes the matter of that private email account she is claimed to have used professionally while secretary of state, and her handling of the murder of the US ambassador in Libya. The latter suggests a reluctance to accept ultimate responsibility, which is not a good recommendation for a president. The former suggests confusion about where to draw the line between the personal and the professional – a line more clearly drawn in US politics than here. Her explanations – most recently to reporters in Iowa, where she talked about “convenience” that turned out “to be not so convenient” – remain unsatisfactory and high-handed.

Most unfair of all is the health question. In her last weeks as secretary of state, Clinton spent a few days in hospital being treated for a blood clot, the prognosis being a complete recovery. When she first mooted running again for the presidency, however, George Bush’s former attack-dog, Karl Rove, cited that incident to sow doubt about her health. He was criticised even by fellow Republicans at the time, but presidential campaigns are ruthless. If she wins the nomination, the health issue will not be off limits.

For Clinton even to consider halting her campaign would, of course, be wrenching, and not only for reasons of personal ambition. As her loyalty to her parents and her wayward husband showed, she is imbued with a deep sense of duty, and duty doubtless plays a role in her campaign. As the one woman with the profile and fundraising capacity to reach the White House in 2016, she would surely prefer to entrust her fate first to the delegates of the Democratic convention and then to the voters of the United States. This would be understandable but misguided. In any pursuit there comes a point of no return, and with a pre-campaign fixture – the Iowa State Fair – out of the way, that point is fast approaching.

She is imbued with a deep sense of duty, and duty doubtless plays a role in her campaign

As it happens, yesterday was the anniversary of Bill Clinton’s public admission of his relationship with Monica Lewinsky. Today is the anniversary of that gruesome family tableau – Hillary, Chelsea, Bill, and dog Buddy – taking the long walk across the White House lawn to the helicopter that would whisk them away to their holiday on Martha’s Vineyard.

In the 17 years since then, Clinton has become the first former first lady to win a Senate seat, and the first woman to be elected as a US senator for New York. These years also included her defeat for the Democratic nomination to the one candidate in a generation whose appeal outstripped hers. And she spent four of them travelling the world as US secretary of state. It is a distinguished and remarkable career, but it is now time to call it quits, while the decision is still hers to make.

She can cite personal reasons (concerns about her husband’s health, for instance), or the hope that she has left time for another woman – the Massachusetts senator Elizabeth Warren, or the health secretary, Kathleen Sebelius – to run. But call it quits she should, unbeaten.