He's the one who has got the most to loose. Not so much his job as of himself.
Look at his face. That has got to be a man who is lying there awake in the middle of the night, and he cant even turn the bedside lamp on because he doesn't want to wake his wife up, and he couldn't concentrate to read even if he did.
And what he is thinking about in the dark is that everything that he thought he'd done for the best might be judged a failure because of his own decisions, and in 100 years time there will still be people writing books arguing about how much he was to blame for a culture that brought the world to its knees.
A few weeks ago, he made a speech feebly blaming "lobbying" and "pressure from the Conservatives" for deregulation of the banks, which suggests he is already beginning to try and find a way to tell himself about his choices, but it will be all the harder to bear the answers because he will tell himself he made the choices in good faith, with good intentions, in order to use the tax revenues to do good.
And now everything that he may or may not have achieved before it will seem uninteresting to history compared to the crash. That's what he is now, as a public figure. The Bankers' Crash, guilty or not?
And that is quite a shift in what he can tell himself about himself in the last 24 months or so.
There is only one job in the whole world in which he can do anything about that, in which he can take action to change the ending of the story written about him, and of the story he can tell himself with any honesty. And that job is Prime Minister.
That is what will be torturing him. That perhaps as soon as tomorrow he's not going to be able to do anything else about changing the end of the story. If he looses the job then all he can do, from his new job at Oxford or Havard or wherever, is wage an undignified campaign for his own reputation, not change the future on which that reputation will rest.
Compared to that, Clegg and Cameron don't have much of themselves at stake. Cameron will probably get the knife if he can't deliver a coalition, but wanting to be the next Tony Blair isn't a failed ambition that anyone would find it too hard to recover from.
And as for Clegg, if he makes a tactical mistake he'll suffer only according to the strength of his principles, which ought to be what guides him anyway. If he follows them, he can't blame himself too much if it doesn't work out, and he's the only one of the three who is certain to be around for the next election with chance to try again.
That's why the big scene is, or has already been, when Brown understands, or is made to understand, that he has to let go, and when he knows that this time there isn't any more fight to be had. To work as a scene you'd have to write it such that he had real self knowledge and honesty, which he may or may not have.
But if the character of Gordon Brown has that self knowledge and honesty, then that is the scene when we'd watch a human being suffer at the hands of the only thing that can't ever be changed, our own choices in the past.