My leading theory for der Fuhrer's behavior in the last couple of debates is that he did some cocaine before each of them. Browsing the net, I find that cocaine (or other "ups" such as speed) can cause the sort of rapid eye blinking we saw. Also Bush's irritability, but who knows what Bush looks like when not irritable? The blinking, though, that's new. And apparently a cocaine high lasts about 20 to 40 minutes, which might explain the way Bush got lethargic towards the ends of the sham "debates," with his speech becoming slurred and so forth.
Cocaine seems to be a drug of choice for Bush, but maybe he also does speed or other drugs he can get with a doctor's prescription.
Another theory comes from once or twice where I came upon the suggestion that morphine abuse can cause eye blinking. I don't think, though, that that's what's going on here.