The Economist says it plain and simple, yet again, in their article on McCain:
If Democrats were to deprive Mr McCain of the chance of running against Hillary Clinton, that would be the cruellest blow. Mrs Clinton would be a one-woman solution to the Republicans’ problems, a guarantee that money will flow into the party’s coffers and that true-red voters will troop to the polls.
They said it months ago, in their article on the Clintons:
If what should be a cakewalk in November turns into a rout, the Democrats will know who to blame.