Barack Obama, rested after a week's holiday in Hawaii and oozing self-confidence, generated a thumping $7.8 million (£4.2 million) on Sunday night from VIP donors at a San Francisco hotel after telling them: “I will win, don't worry about that.”

The Democratic nominee has continued to set a ferocious pace in the dash for cash, announcing at the weekend that his campaign raised $51 million in July, compared with the $27 million that represents the best monthly haul yet for John McCain, the Republican nominee.

He was introduced in San Francisco by Nancy Pelosi, Speaker of the House of Representatives, who hailed him as “a leader that God has blessed us with at this time”. His speech betrayed some of the doubts that have afflicted his campaign in recent weeks as his polling lead tightened to within the statistical margin for error. He has previously been attacked for arrogance after his campaign produced a mocked-up presidential seal featuring a Latin version of his slogan, “Yes, we can”.

At the start of a final week before the Democratic convention in Denver, he cautioned against complacency among his supporters. “American politics aren't that simple,” he said. “The fact of the matter is, at a certain point, when government has not been serving the people for this long, people get cynical. They tune out. And they start saying to themselves: 'A plague on both your houses'. They are willing to consume negative information more frequently than positive information, for good reason - they've seen how promises haven't been kept.

“The race is turning nasty...they know they can't win on the issues. So what they'll do is they'll try to scare people: ‘He's risky. He's risky. We're not sure',” Mr Obama told them before offering an assurance that it would not work.

“Not only do you have a candidate who doesn't take any guff. Not only do you have a candidate who will hit back swiftly and forcefully and truthfully,” he said. “But you've also got American people who are rising up all over the country and saying: 'Enough is enough'.”

His campaign has made much of his small donor base of more than two million people. Official figures show that most of his money is raised at big, high-dollar events.

Mr McCain yesterday emphasised foreign policy, telling a veterans convention in Florida that his rival had “legislated failure” in Iraq. “Both candidates in this election pledge to end this war and bring our troops home,” Mr McCain said. “The great difference is that I intend to win it first.”

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