During the primary it was often remarked upon that while the Clinton campaign was a raucous bunch, always fighting with each other and generally being chaotic, the Obama campaign was very calm: "No Drama Obama" Now its easier to be calm about stuff when you're winning, but even when Obama was down, there was never the panicky chaos that sometimes tripped up the Clinton campaign.
Well multiply that contrast by ten and you have the Obama-McCain race. McCain has gone though at least two major campaign shake-ups. Everybody gets fire shake-ups. McCain make crazy, unpredictable choices. Not just the one time, but over and over and over. Obama manages to resist the panic when he was down in the polls. (And good lord, we Dems love to panic) McCain goes down in the polls and it's hit the big red button time.
Micky Kaus is right (Oh Crap) a McCain Presidency would be exhausting.