In a phone call from Air Force One, the President reportedly told a group of top donors “I can’t do this by myself” and urged them to open their cheque books to “meet or exceed what you did in 2008”.

Noting that most had “maxed out to my campaign last time,” Mr Obama told them: “I really need you to do the same this time,” according to a leaked transcript.

Despite holding a narrow lead over his rival, the president informed the supporters that his ability to campaign and broadcast advertisements in key battleground states such as Florida and Ohio directly depended on their generosity.

Details of the call emerged days after Mr Obama warned supporters that he would be “the first president in modern history to be outspent” by his opponent unless donors upped their contributions.

Mr Romney and his party raised $76 million for their campaign in May, while Mr Obama – who had not been out-raised in five years – brought in $60 million with the Democrats.

Romney aides have boasted that their haul for June may exceed $100 million, after being boosted by Right-wing anger over the Supreme Court’s approval of Mr Obama’s health care reforms.

While he remains ahead overall in the money race for the time being, loose talk of Mr Obama being the first candidate to raise $1 billion has been silenced by the Romney machine.

“In 2008 everything was new and exciting about our campaign,” Mr Obama said, according to a recording of the call obtained by The Daily Beast, a news website. “And now I’m the incumbent president. I’ve got grey hair. People have seen disappointment because folks had a vision of change happening immediately. And it turns out change is hard”.

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