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Former Vice President Joe Biden should be worried after receiving the endorsement of former President Barrack Obama which has been the "kiss of death" for electoral causes in the US says The Australian's Foreign Editor Greg Sheridan.

Mr Sheridan said on top of President Obama's endorsement, Mr Biden also has the support of former Democratic nominee Hillary Clinton, "so with backers like that you'd have to be worried".

He told Sky News host Peta Credlin, although Mr Biden is leading in the polls against President Donald Trump, Ms Clinton was in the same position in 2016 before Donald Trump won the November election.

"Who knows what Trump will do to Biden in the campaign".

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