Power Line explains why Bush had to keep Rumsfeld. I think I agree with almost every statement. The only thing I hesitate to endorse is the suggestion that the left as a whole wants us to fail in Iraq. I do think a large number of left-thinking people secretly want that but would never admit it even to themselves. I think that even drives their criticisms in ways they don't see. The way the claim is put, though, makes it sound as if this is true of every opponent of the war and a complete part of their explicit thinking, which just seems laughable to me.
The thing that seems most clearly true that many people are ignoring is that because Bush really doesn't believe this whole effort was a mistake (and I still agree with him on that) it would be lying to fire Rumsfeld now, because that would send a message that he has accepted the arguments of his opponents that the whole shebang was a mistake. Since he considers these to be bad arguments (and I agree with him), he can't fire Rumsfeld because of the message it would send. That's a side of politics that I consider very unfortunate, because I can think of plenty of reasons he might want to ask Rumsfeld to resign that don't involve admitting failure in Iraq, but the perception will be that he's admitting exactly that. Because he doesn't want to stain what he sees as a truly good effort, he won't do it. I can understand that, even if I don't like the political realities that make it that way.