What percentage of voters in a given election were more than occasional watchers of TV News?
What percentage of voters in a given election had ever listened to the candidates on TV?
I think this is relevant to the question of "charisma" being debated by shag & MP. Tentatively, I would think to win a seriously contested election (most are not such) a candidate's "charisma" would have to be conveyed throug third parties, not directly by the candidate in speeches (or partial speeches on TV news). So what would count would not be favorable response to a candidate's speech but whether or not that favorable response would be projected into conversation with others who had not heard/watched the candidate.
The audience for a given speech, I would presume, ismade up overwhelmingly of those who have already decided to vote for that candidate. Hence the speech cannot change any votes, it can only inspirit the listeners to go out and change votes.
Carrol