Who controls the LSM? Enough information exists in McCain's public record exists to pretty well sink him, and Hillary probably has some confidential information which could do the job thoroughly. If a candidate tries to bash another candidate with his record, that will often cause some voter resentment against the candidate doing the bashing. But if the LSM does it, there would be no such backlash.
Perhaps it's really the LSM that are more important than the Democratic leadership, but when the LSM does something it's usually a pretty safe guess that the Democratic leadership doesn't object too strongly.
OK. So how did Bush get elected, not once but twice?