you dissed who?

Letterman on McCain's no-show:

"Somebody's putting something in his Metamucil"

"This just doesn't smell right. This is not the way a tested hero behaves."

But McCain wasn't in Washington to fix things. Instead he was
A) Answering for Katie Couric on CBS [same network]
B) In the same city as cancelled appearance, [New York]
C) In the same time slot at Letterman [11:45PM]

Look's like the white man is running scared.
But more importantly, why would someone dis Dave?