As addendum to the earlier post, unlike its predecessors in the Number 2 Party slot (the Socialists and Shinshintō) the DPJ's problems are not structural. For the Socialists in particular, no matter how hard they tried, they could not win.
The DPJ's problems are largely volitional--even now, party members do not know what it is that they are trying to do.
I agree with the speaker of yestereve: the first thing they have to want to do is win.
This post has been edited for clarity.