Republicans are going through a very rough patch right now. Public approval of the party, and morale of the party faithful, are both at record lows. E. J. Dionne wrote a recent column about two books where you can find Republicans struggling with the future direction of their party.
So, with the Republicans in such disarray, this is the best chance that the Democrats have to win the presidency since the post-Watergate election of 1976. All they have to do is coast to victory. The best that McCain can hope for is if the Democrats do something really stupid to screw up their chances. But, every day that goes by without the Democrats choosing a nominee looks more like McCain might get just what he needs--the Democrats shooting themselves in the foot. David Brooks does a good job of laying out one possible scenario, which would lay the blame mostly on Clinton. (I laughed out loud at the line, "she possesses the audacity of hopelessness.") But, there's more than one way for the Democrats to screw up their chances.