Engaging in classic horse-race punditry (that is, wildly generalizing from a single incident for the sake of sensationalism): Could Oprah Winfrey's endorsement of Obama hurt Edwards--and not Clinton--the most (if it really hurts anyone at all...)? A NYT anecdote (e.a.):

Kate Anderson, 20, a student at the University of Iowa in Iowa City, said she loves watching Oprah and that she and her mother “religiously read everything she has to say” in her magazine. She said she likes Mr. Obama and while the endorsement is not the only reason, it is part of the reason.

“I think what Oprah stands for to me is a sense of moving forward and hope, which I think is what Obama has come to stand for,” she said. Ms. Anderson said she was torn between John Edwards and Mr. Obama, “and I still kind of am, but I’m leaning more towards Obama, and that’s because of both Oprah’s support and what I’ve seen of him.”

Sounds ironclad to me! Edwards himself talks a lot about "moving forward"...