A senior adviser to Barack Obama has blamed recent attack advertisements comparing the Democratic presidential hopeful to celebrities Britney Spears and Paris Hilton for a dip in Mr Obama's polls with voters.

Tom Daschle, the former Democratic Senate majority leader, said in an interview with the Financial Times that the Mr Obama's Republican rival John McCain was seeing a "short-term blip" as a result of the advertising, including one that used the image of Charlton Heston as Moses to mock the supposedly messianic Mr Obama as being "The One".