for example, http://en.wikipedia.org/wiki/Lincoln%E2%80%93Douglas_debates
The format for each debate was: one candidate spoke for 60 minutes, then the other candidate spoke for 90 minutes, and then the first candidate was allowed a 30-minute "rejoinder." The candidates alternated speaking first. As the incumbent, Douglas spoke first in four of the debates.
Those were 3 hour debates. Now all a politician has to do is look good holding a football.
(this is basically paraphrasing Neil Postman's work from http://en.wikipedia.org/wiki/Amusing_Ourselves_to_Death)
Amusing Ourselves to Death: Public Discourse in the Age of Show Business
Sure, because Obama won we declare him the most charismatic candidate. Had he lost, people would say the oposite, declaring him 'professorial' 'aloof' or 'elitist' (all criticisms directed at Obama at times in the media) and point out his lackluster performance in the first debate as evidence of a lack of charisma.
Perception of charisma is also heavily influenced by our personal biases. I'm sure that we perceive candidates we like as being more charismatic. I bet a majority of Democrats would say Obama is charismatic and a majority of Republican would disagree.
Bush and Clinton were charismatic in ways that both sides of the aisle could easily acknowledge. Charisma is a pre-req to being president, and is not conveyed on victory.
If Gore would have won in 2000, that would have been very interesting, since he really wasn't at the level of Bush on likability, he would have been the least charismatic president since...Johnson, Nixon, or the way Carter actually turned out.
Bush Sr. is the weakest point of the theory. He's pretty flat however you look at him. But Dukakis wasn't exactly Marlon Brando or anything. I don't think the theory could have won either way with those two.
Words tossed around when he started his campaign were "efette", "wimp", and "unmanly". Obvious slurs, but he had a lot of public perception to get over.
People in the media have been saying that regardless of his performance.