Regarding the Bill Richardson endorsement of Barack Obama, Peggy Noonan made a good point on Meet the Press, yesterday.
Essentially, she pointed out that the Clintons have had this sort of "voodoo thing" which makes them seem invicible. Her argument is that the Richardson endorsement, in essence, cracks that facade and allows Obama supporters to believe the Clintons can be beaten.
As a Baltimore Oriole fan (if such a thing is possible) I appreciate this phenomenon more than most. The New York Yankees, for example, seem to have this ability to miraculously snatch victory from the O's at the last minute (remember that kid, Jeffrey Maier who stole that playoff game in '96?) Needless to say it is a psychological detriment to believing that -- at any moment -- you are going to blow it.
Regardless of what you are doing, it is obviously important psychologically to at least believe you can win -- and that your opponent isn't ordained to win. It could be that Bill Richardson's endorsement is the first step toward cracking whatever is left of the "Hillary is inevitable" psychology.