Mark McKinnon, a media strategist and former McCain adviser who worked for both of Mr Bush’s campaigns, said of the advertisements: “I think they’ve crystallised their message and I think they’re hitting a nerve.”

Political advertising is effective, he added, when it ties into an overall narrative. In this case, the message has been framed in a positive and negative way: that Mr McCain puts “country first”, while Mr Obama puts “Obama first”. The theme was repeated in a McCain advertisement rel­eased on Wednesday, showing flashing cameras and crowds chanting “Obama” as a voice asks, “Is the biggest celebrity in the world ready to help your family?”