That's according to a source quoted in the The UK Sun:"Joss is a big supporter of Barack Obama and was very excited to be asked to do this for him. He sent a personal message asking her to get on board. He has always admired her music and thinks she is the perfect choice because of her unique appeal to black and white voters. She believes he is going to be the first black American president and she is honoured to be a part of that."
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