Praising Mrs King’s courage in the pursuit of justice for black Americans, Mrs Clinton said that her example posed a similar challenge to her compatriots: “Will we say, when the call comes, ‘Send me’?”

There cannot have been anyone in the New Birth Missionary Baptist Church outside Atlanta, including her husband and three other US presidents, who did not think that the question had a very specific double meaning. When the call comes in 2008, will the Democrats, and the nation, send her? But the seemingly unstoppable Hillary bandwagon has begun to show its first real signs of wear in the p ast few weeks.

The former First Lady and political lightning rod for conservatives has barely put a foot wrong since she was elected to the Senate from New York six years ago. She has moved rapidly to the centre on controversial issues such as abortion and gun control. She has established a reputation as a hard-working legislator, protecting the interests of her constituents and demonstrating an impressive command of policy. She has cast herself as a national security hawk in a time of crisis — voting for the Iraq war, and even attacking President Bush for being soft on Iran.

But the myth of her invincibility has recently started to unravel. Her aggressive stance on national security has landed her in mounting trouble with the Left of the Democratic Party, which has become stridently anti-war in the past year.

A deft political touch seems to have deserted her on several occasions, most recently when she accused Republican leaders in Congress of behaving like “plantation owners”.

Above all, the issue that her supporters and opponents alike consider her biggest liability has surfaced ominously: the likeability factor.

Few deny that Mrs Clinton is razor-sharp and politically savvy. But even supporters worry about her personal skills, at least before a large audience. She is a somewhat wooden speaker with a hectoring style at times more reminiscent of Al Gore than her husband. And unlike Bill, she projects a lofty, distant air that has been likened to the Queen of Sheba in a power suit.

Last weekend Ken Mehlman, the Republican National Committee chairman, homed in on Mrs Clinton’s personality, saying that she was too angry. His aim was both to pinpoint her weaknesses and to needle her, and it seems to have worked. She retorted that Republicans had resorted to personal attacks because they could not defend their own record. An opinion poll suggested last month that Mrs Clinton would lose a putative presidential election against the Republican John McCain by 52-36 per cent. It is absurdly early to begin taking polls seriously, and Mrs Clinton continues to have powerful advantages, at least in the fight for the Democratic nomination.

She has instant name recognition. She will raise unprecedented amounts of money — and already has $10 million (£5.7 million) in the bank for her Senate re-election campaign this year. Changes in the Democratic primary calendar could help her by reducing the early importance of small states, where face-to-face encounters with voters can be decisive.

But the doubts have intensified as the reality of a presidential campaign draws near. Some Democrats are looking urgently at other potential nominees; several former Clinton White House officials have been coaching Mark Warner, the former Governor of Virginia and an increasingly serious challenger.

At Mrs King’s funeral — a thinly disguised political rally — Mrs Clinton’s greatest strength and greatest weakness was on display. Her own remarks were preceded by her husband’s eulogy. The former President was on characteristically bravura form. In a tailor-made setting, in an accent several degrees south of plush Westchester County, the New York suburb that he now calls home, he was alternately funny and moving.

Mrs Clinton was, once again, in her husband’s shadow. It is a shadow that has nurtured and shielded her for years, allowing her to benefit from his raw political skills. But it is also a shadow that, for many Americans, darkens Mrs Clinton’s reputation, reminding voters of the sleaze and scandal of eight turbulent White House years.

The hope in her camp is that people will believe that Mrs Clinton has her husband’s political strengths and none of his weaknesses. The growing fear is that she incites the same level of loathing and suspicion as her husband always did, but has none of the charm and personality to deflect it.

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