Progressive blog traffic and possible impact due to support for Obama or Clinton:
AmericaBlog, Kos, Eschaton (considered neutral), Talk Left, and MyDD are examined
for the month of March. Although the pro-Obama blogs (AmericaBlog, Kos) have seen a decline, on the whole the traffic has been fairly stable for all of them. It's likely that people already gravitated to blogs early this year based on subtle clues that they were pro-Obama or pro-Clinton. Once there, why go to another blog that denigrates your favorite?
Uhhh... because it has something else to offer as well?
The fact that TalkLeft is pro-Clinton is less of an influence on my reading them than the fact that there's been little else being offered there lately. YMMV.