Yes, all that Choom Gang Ganja has his brain demented and babbling. You are brilliant for pointing out that it was mockery, not the failings of an 82 yr old Clint.
What Clint did was an art form that I don't think people are still getting their arms around....
* It was the Artist Stagecraft, something you might only get at a high end drama training session in College, a push the envelope exercise of your mind and talents.
* It was not only Acting but Humor, maybe Poltical Satire at it's finest.
* The Metaphors of the empty seat i.e. Obama's empty promises, empty suit, the missing President, the dimished POTUS, etc etc etc are endless, we as Freepers' could brainstorm them for thousands of post...
The more we think about it, and replay it on the web, the more we see, we will be talking about this for quite sometime...
It was a unique for a political conventions and as it will turn out, devastatingly effective.