One of Sarah Palin's former political foes has delivered a warning to Joe Biden before tonight's first televised vice-presidential debate: underestimate her at your peril.

The Alaskan state governor and moose-hunting "hockey mom" plucked from obscurity by the Republican nominee John McCain has been getting intensive coaching ahead of the debate from experts including the former Secretary of State, Henry Kissinger.

Republican concerns grew after interviews in which Ms Palin, 44, has appeared lost for words and supporters feared that a poor performance could deal a lethal blow to the McCain campaign in the same way that her performance at the Republican convention breathed life into it.

Her gaffes include citing Alaska’s proximity to Canada and Russia as giving her foreign policy experience.

But Mr Biden - who famously came a cropper during a primary debate in 1987 when he borrowed a line from the British Labour leader Neil Kinnock without crediting it - will be careful to avoid complacency, especially after an account in today's Los Angeles Times of Ms Palin's success in Alaska.

The newspaper said that Ms Palin had been "woefully unprepared" when she started her run for the Alaska governorship in late 2006, stumbling in her answers before an audience of electrical workers

But within a few weeks she was much more at ease and, in the words of one observer, she ended up flummoxing her rivals "like Muhammad Ali dancing around the ring".

"She distilled policy questions into simple answers and countered her opponents' attacks with verbal thrusts delivered with a sunny smile," the LA Times reported.

Her rivals in the campaign were the incumbent, Tony Knowles, and Andrew Halco, a businessman who ran as an independent. Both considered themselves to have a much better grasp of issues and policy, but Mr Halcro told the newspaper that was not much use.

"When you try to prove she doesn't know anything, you lose, because audiences are enraptured by her," he said. "And her biting comments give you a sense of how competitive she is. Anybody who doesn't take her seriously does so at their peril."

Not that Mr Biden, a 35-year Senate veteran, does not face his own problems. He has been called uncontrollably verbose and a “gaffe machine,” and was even asked in a Democratic primary debate if he could control those qualities with “the discipline you need on the world stage".

He also faces the prospect of being eclipsed in tonight's showdown at Washington University in St Louis by Ms Palin’s star power.

“Biden is in a difficult situation,” said James Pfiffner, professor of public policy at Virginia’s George Mason University. “He is someone who knows an awful lot about foreign policy... but the star of this show is clearly Governor Palin.”

At least two renowned conservative columnists keen to back Ms Palin when she was announced as McCain’s running mate have changed their minds and decided that she is not qualified for the job, and analysts said that tonight's debate could seal her candidacy.

“It’s make-or-break for her in the sense that, in a three-game series, her record so far is one and one: the convention and the interviews,” said Peter Kastor, Washington University history professor, “This could be what seals the deal. If she does extremely well or extremely poorly, obviously it will be the debate that people say defines Sarah Palin’s candidacy.”

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