I think the only thing that could defeat McCain is his age, or Iraq blowing up. Or Orsome huge snaffu over the horizon none of us can see--which is always a possibility for any candidate.

If McCain can beat back the age issue by maintaining really good health through November, and he makes a good choice for VEEP (ie, someone younger, rigorous, moderate and somewhat independent of Bush/Cheney and Pat Robertson sort of ideology), I really do believe he is a shoe-in against Clinton or Obama.