One reader offers this explanation for the rift:
I am convinced that the reason the lefty bloggers have turned on Obama is that he created, independently of them, his own grass roots and "net roots" network of small contributors and part-time activists. Kos and his ilk started to believe that he could snap his fingers in favor of a particular candidate, and scads of small contributions would start flowing toward that person. Obama reminds me of a DJ who was on a San Francisco powerhouse rock station, who would sign off his morning show with, "If you don’t like the news, go out and make some of your own." Obama decided to go out and make his own grass roots network rather than pander to the Kossack wing of the Democratic party. That is a direct threat to his power, and he wins, it will be another salient benefit of his candidacy.
The Dish 