I suspect this
link has already been posted and discussed but I can't find it. I think it is a fair analysis of why Dean faded so abruptly. Basically, it says that the strength was never as real as we all imagined. It also says that Dean himself was a problem. I think many things are partially to blame for Dean's demise including the candidate, his supporters, his opponents, and the post Thanksgiving media coverage. However, the linked analysis seems a worthy addition to the list. I'd add that if you accept this analysis even partially then it begs the question of how do we do things differently next time? Or how do we use the power of the net even more effectively?