The answer is to be found, like so much wisdom, in the Blues Brothers: it is the politician's instinct always to "get the band back together again". Every political leader establishes a gang that gives human form to his psychological comfort zone. Members of the gang come and go over the years; new members are cautiously admitted. But the politician will always revert to the tried and tested core of the original gang if he can.
After his disgrace as a lobbyist promising access to government in 1998, Derek Draper said goodbye not only to the Labour Party but to politics: he trained as a therapist and wrote extensively of his newfound happiness away from the dark arts of the political world and what he called his "idiot years". And yet it took little to tempt him back into the milieu as Labour web strategist - very well-connected, as we now know, with the Brown attack machine at Number Ten.
No wonder Alastair Campbell - the man who keeps coming back - has disowned McBride. The incestuousness of the gang must be concealed, because it is its primary weakness. Where is the new talent? There is none. Not really. Whatever Blair and Clinton claimed to the contrary, the truth is that you can't renew in office; and the deep psychological reason is that you don't really want to.