Fox showed a video of the event at which Cassidy was supposedly incoherent. He was speaking at some public event several months ago and apparently lost his train of thought for a few seconds. As Cassidy himself said (he was being interviewed by Megan Kelly on Fox) they took a two-second clip out of a 15-minute speech.
I don’t think there is anybody who, at some point, doesn’t stumbles over something. If we were to adopt a standard of stumbling speech, however, we should meter the stumbles and, so, compare the rate of stumbling of different people.
For Mary Landrieu to say that an obviously intelligent person isn’t intelligent because of an occasional stumble merely reveals that she is an ignorant buffoon, and desperate, and it doesn’t change the fact that she looks like the second coming of Miss Piggy.