What are the chances of Prime Minister Kan surviving the September election for the DPJ leadership? Still good, though I now see a plausible scenario in which another person emerges to replace him. However…
Ichiro Ozawa is not going to challenge Kan directly. There’s no upside for him. If he loses, which would be by far the likely outcome, he’ll be finished as a central political force. If he wins—it’s highly unlikely, but the possibility cannot be dismissed—he’ll have to serve as prime minister. Case closed.
Would an Ozawa surrogate succeed? No. Everybody not in thrall to Ozawa (or owe him one, the two are not mutually exclusive) will fear the mass media implications of a strong, public association with him.
This leaves the chances of a multiple-candidate challenge that leaves the non-Ozawa vote divided between multiple candidates, with Kan being only one of several of his peers. As the voting results come in, Kan will have no choice but to resign, leaving the door open for one of the non-Ozawa candidates to emerge as the majority candidate over the Ozawa surrogate. (If Kan can’t make it on the first round, he’s almost surely a dead, not lame, duck.) Of course there’s always the possibility that the Ozawa candidate will make such a strong showing that the DPJ has no choice but to select him/her. The equivalent of an exit poll for the 400 local votes (in addition to the two per-Diet member votes) could also influence DPJ Diet members and grease the way for one of Kan’s challengers to take over.