The image of a shark dying because it has stopped moving forward appears in James Forsyth's account in the Spectator. Its being twittered to and fro. But it misses the main point. Cameron positioned himself as the heir to Blair which was a mistake. But he also had one side that was not Blairite, while modern, smart and socially progressive he claimed he was even more Euro-Sceptic than David Davis, which is saying something (and won him the leadership). The he renaged on holding a referendum on the Lisbon Treaty. It's beside the point that it would have been 'pointless'. The real point was that he should have kept his word and said 'up yours' to Westminster et al. Then everyone would have know he was 'different'. When the dust settles and people look at the stats I bet there is a correlation between Cameron's support weakening and his dumping his promise of a referendum.
PS: But the left is foolish to bang on about the Tories not being different. See David Marquand in the NS for the theory and this from the new Tory MP for Norwich North, Chloe Smith talking about books with Total Politics. I can't believe there are many Labour MPs who'd give such attractive and interesting answers (allowing for one party political slip re John Major)