I'm no fan of Arlen Specter, but accusing the man of dementia is both wrong and counterproductive. Posting a video that shows him losing his train of thought, and then asking people to accept it as proof of dementia recalls Bill Frist's "diagnosis" of Terry Schiavo, also based on mere video evidence. And Frist, at least, is a doctor. An asshole, but a trained medical professional.
I'm a Hodgkin's survivor. I had it when I was 30 years old. Chemo and radiation. It took a year for me to regain my full energy. It took months for me just to be able to walk normally, again. I'm not saying that what's revealed on the video was caused by Specter's cancer treatments, but I am saying it's possible. But I'm not a doctor. And one video and some other anecdotal evidence would not be enough to make a diagnosis, even if I were.
We are supposed to be the reality based community. If we can't win elections without resorting to hyperbolic smears, we don't deserve to win those elections. We don't change politics by becoming that which we abhor. We win by being right on the issues, and by elevating the process. If we aren't the change we want, there will be no change that we want.