Gordon Brown was on BBC news earlier looking very bedraggled and, frankly, knackered. Tie askew. Double chin well showing - or is that a triple? The man couldn't relaunch a dinghy, let alone his premiership. He's doing worse than Callaghan. That's saying something.
The basic problem is that he lacks a section of intelligence. Call it "emotional intelligence" if you like. So that, he seems incapable of sufficiently showing empathy towards people, so that he is incapable of leading. In comparison to Blair, this shows up very sharply. You can't imagine Brown doing a "Princess of hearts" can you? He replaces this lack of empathy with people by withdrawn moods and "tempers of an indescribable nature" (Frank Field's words)
To put it bluntly, he won't be a success as Prime Minister as long as he has a hole in his bottom. This is a shame because if you take his chancellorship (minus the last budget) he was one of the most successful chancellors in the history of this country.