Robocalls replay Clinton attack

But the last-ditch Republican attempt to warn wavering voters away from voting for Barack Obama is focusing ruthlessly on his one proven Achilles heel - lack of executive experience.

As the polls tighten in key states such as Florida and Pennsylvania, both campaigns are focusing their arguments on the pros and cons of long service.

In an automated telephone call to targeted voters in swing states, the Republicans have played a recording of Hillary Clinton mocking Obama's lack of experience when she was running against him for the Democratic nomination.

In comments reminiscent of Gordon Brown's conference attack on David Cameron as a "novice", Mrs Clinton says: "In the White House, there is no time for on-the-job training. Senator McCain will bring a lifetime of experience to the campaign, and Senator Obama will bring a speech that he gave in 2002."

Mrs Clinton's camp are furious at the use of her remarks in what they say is an altered context; she has been campaigning for Mr Obama and is expected to benefit from an Obama presidency, possibly with an elevation to majority leader of the Senate.

The "robocall" technique is aimed at worrying undecided voters about Mr Obama's limited record as a senator. Sources on the McCain team have said that he is pinning his hopes of a late comeback on a combination of motivating the Republican base and adding enough Democrats who backed Mrs Clinton but have not transferred their allegiance to Obama.

"It isn't a done deal," said one source. "Senator Obama has shown himself by far and away the better campaigner but it is harder for him to prove readiness for office. That is what Mrs Clinton meant then and it is no less true today."

Mr Obama sought to turn the experience charge on its head, by mocking the unpopular vice president Dick Cheney's last-minute endorsement of Mr McCain. The Republican candidate has striven to shake off his associations with the Bush White House, emphasising his independent record.