Why *some* of the candidates don't answer the question asked by the moderator or host.
I'm certain you've noticed that a specific question about policy will be asked to a candidate during a debate or an interview on a cable or morning news show and the "answer" isn't an answer. It's something else. And you wonder what just happened.
Especially with the slate of republicans, logical fallacies are employed. They say stuff that is not only off-topic, but also fallacies like "missing the point", "red herring", appeal to authority, appeal to emotion. Words that are meant to confuse, divert, and manipulate people to first support, then vote for that candidate.
And Trump, Cruz, Carson, and Co. are not stupid. They know exactly what they're doing with complicate moderators and/or hosts who do not hold their proverbial feet to the fire with follow up.
Below are links that list commonly used fallacies. Print them out and use during the next debate and see if you can identify which ones are being used.
http://writingcenter.unc.edu/handouts/fallacies/
http://utminers.utep.edu/omwilliamson/ENGL1311/fallacies.htm