Steve Hildebrand describes himself as a “big fat goof” who is scared of flying. But, as the chief author of Barack Obama's grassroots strategy, he is helping to rewrite America's campaign rulebook.

While Hillary Clinton has won most of the key contests that she has made a priority, Mr Obama is leading the race for delegates because he has picked up most of the other states. “We have competed in large and small states — primaries and caucuses — and not let any state go by,” Mr Hildebrand explains in an interview with The Times. “It's beyond me why the Clinton campaign did not do the same.”

Mr Hildebrand, 45, noted that Mrs Clinton largely turned her back on states that held caucuses — events with smaller turnouts where an organisational edge counts for more than in primary elections. Indeed, after spending up to $25 million (£13 million) losing in Iowa, she has railed regularly against the “unrepresentative” caucus concept. The result was that in the last eight caucuses Mr Obama picked up 209 delegates, compared with her 96.

When Mrs Clinton won New Jersey, which has a population of 8.7 million, rules that required delegates to be awarded proportionately meant that she made a net gain of just 11. By contrast, Mr Obama's huge margin of victory in Idaho — population 1.5 million — earned him 12 more delegates than Mrs Clinton.

Mr Hildebrand had set up five campaign offices in Idaho by last autumn, an unprecedented effort for a reliably Republican state that is usually ignored by Democrats. The benefits could be seen even before the vote on February 5, when Mr Obama staged a rally in Boise that was attended by four times more people than the entire turnout for the 2004 caucus.

Mr Hildebrand says that much of this is because of the swelling wave of enthusiasm washing across America for Mr Obama, reflected in massive fundraising from hundreds of thousands of small donors. “That has made such an incredible difference for us. Everywhere we open a campaign office, the volunteers just flood in and ask what we want them to do.”

He recalls an event a year ago in Austin, Texas, “where we put together a rally out of a book club for Audacity of Hope [Mr Obama's bestselling memoir] and three or four hundred showed up. Most of them had not been involved in politics before but were just struck by something about this guy.”

In contests such as South Carolina, Mr Obama eschewed the time-worn technique of seeking the backing of established black community leaders and offering them “walk-around money” to mobilise votes. “Some of the ways that Democrats fought elections in the past, we just didn't want to do,” Mr Hildebrand says.

To the columnist Joe Klein, Mr Obama can sound self-referential — to the point of insubstantial — about this high-minded candidacy. “The Obama campaign all too often is about how wonderful the Obama campaign is,” he said.

But the mechanism is also the message for Mr Obama, whose grassroots campaign reflects his view that change comes from the bottom up — and that Democrats must win in Republican states. Mr Hildebrand describes this as “Barack's organisational philosophy and belief as a national leader”.

Mrs Clinton has recognised belatedly that she cannot allow Mr Obama to continue gaining easy wins and is pouring resources into Wisconsin before Tuesday's primary. Mr Hildebrand responded: “We've had staff there for five weeks.” Although insisting that the battle is far from over, Mr Obama's campaign appears substantially more harmonious than the Clinton camp, which has undergone a shake-up this week amid reports that some of the senior advisers — known as “The Five” — are falling out.

Mr Hildebrand is at pains to give credit to the leadership of David Plouffe and David Axelrod in the Obama campaign, as well as to a team of organisers “who are a lot smarter than me”. He says: “I don't want to be like Karl Rove. One person in politics does not have that much influence on anything. Rove built an image for himself as the guy who got Bush elected twice. Sure - and then they went forward to destroy this country.”

When Mr Obama's advisers started to consider a run for the White House in November 2006, it took a “big leap of faith” to put together an insurgent campaign “with no donor base up against the Clintons”.

But it is a measure of how far they have come that Mr Hildebrand says: “We always hoped it would look something like this.”

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