It is scarcely a fortnight since Nancy Larson announced that after much agonising — and despite a “heartbreaking” last-minute plea from Chelsea Clinton — her super-delegate vote would go to Barack Obama. Now she is not so sure.

“Our role is to keep gauging and re-gauging what the public wants. Although I’m comfortable with the decision I made, there is nothing to stop me changing my mind,” said this Minnesotan yesterday.

She cited how the controversy of Mr Obama’s pastor, the Rev Jeremiah Wright, “keeps cropping up” and said that his comments over bitter small-town Americans “may bother some voters”, saying: “We have to ask ourselves who will be able to go the distance when it counts in November. We have a big responsibility.”

Ms Larson is one of the 795 members of the Democratic Party elite — the super-delegates — who could yet wrest the nomination away from Mr Obama, who is so close to winning this prize that he can almost touch it.

No one doubts that he will claim the larger slice of elected delegates. Mr Obama has also had the overwhelming bulk of super-delegate pledges over the past couple of months. Even in this traumatic week for him, he has had six endorsements, compared with four for Hillary Clinton.

Yet almost 300 super-delegates stubbornly sit on the fence. Some are said to fear retribution from the Clintons, who are not shy of reminding them of favours done. The Governor of New Mexico, Bill Richardson, has already been denounced as a “Judas” for pledging himself to Mr Obama.

Others, particularly those sitting on thin majorities in Congress, hesitate because they do not want to alienate any section of the Democratic electorate. And, even though dozens of Congressmen have privately made up their minds to back Mr Obama, many appear to be waiting for proof that he really is the candidate who will deliver them the White House.

Successive missed opportunities to finish off Mrs Clinton — in New Hampshire, in California on Super Tuesday, in Ohio last month and then in Pennsylvania last week — have reinforced doubts about whether he can transcend divisions of race, class and age that scar American society.

The extraordinary spectacle Mr Wright made of himself this week has opened up further questions about the judgment and, perhaps, honesty of a candidate who says that in 20 years of sitting in the pastor’s pews he never heard him deliver such “rants”.

While some took comfort this week from Mr Obama’s furious renunciation of Mr Wright, there were plenty who felt that it had come more than a month too late. Eileen Macoll, an uncommitted super-delegate from Washington State, said that the controversy was “beginning to reflect negatively” on the candidate.

Mrs Clinton hopes to persuade super-delegates that they must exercise independent judgment by, if necessary, defying the wishes of Democratic primaries and caucuses. Overtaking Mr Obama in the popular vote, as well as winning Indiana next week, could provide them with the excuse they need. Mr Obama’s campaign wrote to super-delegates last week emphasising his claim to be the most electable because he can put into play states from the West that were long ago written off by the Clintons.

But most super-delegates are not big shot politicians who might be expected to enjoy all this attention. Maine’s state Democratic Party chairman, Sam Spencer, is among the as yet uncommitted who view the prospect of exercising influence on the outcome of the race with distaste.

Bombarded daily with calls from the Obama campaign and friends from his days in the Clinton White House “who are suddenly anxious to catch up after seven years”, Mr Spencer said that voters in Maine have concerns about both candidates. He suggested that his vote may be ultimately be conditional on the loser being offered the vice-presidential ticket.

Kansas’s Democratic chairman, Larry Gates, said that “some people think I’m hiding under my desk” by refusing to declare for Mr Obama, who won the state caucuses in February by a wide margin. But he added: “I have valid reasons for staying neutral.”

These include ensuring that Clinton supporters are “back in the boat, rowing in the same direction as the rest of us” in the autumn elections. He also says it is possible that if Mr Obama continues to ship water he may have to do “what’s best for the party” and ignore the Kansas caucus results.

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