One of the things most frustrating about watching televised debates is that they're so carefully staged that you rarely see anything worthwhile. Sometimes, a candidate is completely retarded--see, O'Donnell, Christine--or a bit out there--see, Stockdale, John, 1992 VP debate--and you get some good memorable show. Sometimes a candidate makes the mistake of walking into their opponent's trap--like in 1988 when Dan Quayle made a comparison of himself to JFK, giving Lloyd Bentsen a chance to tear him apart with "you're no Jack Kennedy!" At that, Quayle was too stunned to have any witty retort ready.
But usually, it's simply moderators asking common questions, and candidates using canned responses. If the question is a particularly tough one--such as, "how can you cut taxes, have no real spending cuts, and still keep the deficit low?"--the candidate will use a fluff response like "get rid of waste!" which of course implies that his/her opponent just loves waste too much to cut it. Or if the question is pointed--"how do you explain your family values stances with the time you spent at that orgy?"--the candidate simply doesn't answer the question--"I think the issues of the economy are more important, which is why I favor tax cuts..."
How to make the debates a better test of a candidate?
1) Let candidates ask questions to each other directly. The moderators are too concerned with being fair and don't want to be seen favoring one side over the other. The candidates, on the other hand, will definitely ask the toughest questions to one another. It'll give viewers a chance to see how they'd respond to direct confrontation.
2) Require the moderator to keep pressing if the question isn't answered. If the candidate tries to weasel out, then it's "I repeat my question. You will answer it or you will say "I don't know'."
3) Make it a challenge--the answers to the questions could have rules. Like "your answer must be done in haiku form." "Your answer must rhyme." "You have to work the words 'Roman Empire', 'grass skirt', and 'tumbleweeds' into your answer, coherently."
4) Add a bit of civics quiz to see if these people know much about the jobs they seek. Not just "can you name a recent Supreme Court case" but "can you name the nine justices on the Supreme Court" or "can you name at least three secretaries of state" or "name one country we're not allied with but used to be" or "tell me what NATO stands for".
5) Have a fake assassin stage an attack and see how the candidates react to the threat. It'd be telling if one tries to wrestle the assassin to the ground and the other tries to hide behind his wife in the audience.
6) Show off their talents, by asking each candidate to do an impression of their opponent. This can be educational, by getting each candidate to demonstrate what they think their opponent's arguments are really like.
7) Instead of boring suits, ask the candidates to show up dressed as their favorite historical figure or rock star. Yes, that might mean seeing Barbara Boxer dressed as Paul Stanley from KISS, but we'd also see Sarah Palin do her best Meat Loaf impression.
8) Install a laugh track and have it going after every line, even the ones not intended to be funny.