Why do they want the job in the first place
The trouble with politicians is that they are never happy with the job they have got. They always want more power but the thing is when they get it they find out that it isn't all fun and games. You can hardly blame the Iraqi PM
Nuri al-Maliki for wanting to step down, his country deep in civil war. He may be Prime Minister of his country but it can't be a life affirming experience when your country is tearing itself apart before your eyes and there is very little that you seem to be able to do about it.
This brings me on to
Ming Campbell, who by common consent was one of the better Lib Dem front bencher. True it is not a field where competition is very fierce but none the less he was better regarded than Lemsip Opik amongst others. Personally I can't see why he wanted to be leader of the Liberal Democrats, it's more work, more scrutiny and your ability to change the world is still just about zip.
I don't want to damn him for being old, both Gladstone and Churchill have been PM, a position of responibility far greater than he is ever going to attain and at much greater age than he is now. It's just that he is useless as a leader and would be having a much better time of it if he had never run for the job in the first place. Perhaps this is one of the reasons that all political careers end in failure, not knowing the limits of your abilities.