What makes Arnold run?

Reader Joshua Sharf offers a far more penetrating analysis of why Arnold decided to run than I did yesterday when I suggested he wanted to take advantage of the short campaign period. Sharf has this to say:
“I suspect that there’s more than just the short campaign appealing to Arnold right now. He wasn’t ready in 1998, nor could he have realistically run in 2002. Riordan was running, and it would be his friend’s last shot at the statehouse. Arnold used that campaign for his after-school programs, a little silly [project], but it marked an entry into politics in a personal way, and got people used to seeing him in the political arena.
If he now waited until 2006, he’d be facing one of four possibilities, all of which held specific and greater risks than this election does. An incumbent Bill Simon would likely not be vulnerable to a primary challenge, and if Arnold’s a good party man he wouldn’t challenge him. An incumbent Cruz would likely be able to take credit for an economic turnaround he had no part in, and would have the advantages of inumbency. An incumbent Dick Riordan might or might not run again at 76. An open field, following a termed-out Davis would be too unpredictable.
By running now, he faces an unpopular Governor on his own terms, no Richard Riordan, a Bill Simon weakened by defeat just last year (without having time to rebuild himself), and a Lieutenant Governor who’s almost as much of an unknown politically as he is, but without the star power. And why wait for Davis to be termed-out when you can help him out the door?
I’ve no doubt that the short campaign played a part in his decision, but I think the above scenario is a much bigger part of his calculation.”