And be sure to notice whenever they to ignore the question and answer a different one instead; that means they couldn't answer the original question.

Interacting with the media 101: when they ask you a question that sounds confused, they're probably just asking you to explain the obvious thing (that they don't understand) - so ignore their question and explain that. My point is that this isn't as good of an indicator as you think it is since politicians, almost by definition, already know how to deal with the media.

On the other hand, this bit of media wisdom is supposed to be for a scientist explaining her work to the media, so maybe politicians don't do this at all.