This is a question I’ve pondered before, but my colleague Jon Baldivieso adds some interesting thoughts:

I think [Dean and MoveOn] worked because they gave a voice to the seething discontent (in about half of the country) that had been building since Bush came to office. While Dean and MoveOn clearly made many intelligent decisions over the course of the election season, they would have been nothing without the scope and the intensity of the anti-Bush left.

I think that’s largely missing from the environmental movement. There is enough of an infrastructure in place to give people an outlet for their environmental urges; there’s no buildup of latent, unchannelled outrage the way there were for the political scene in the last 4 years.