What you describe sounds like dodging the question:
Question dodging is the intentional avoidance of answering a question.
(https://en.wikipedia.org/wiki/Question_dodging)
In the context of politics, another word for this kind of trick would be pivot (it's a noun, but I think you can verb it):
Brett O'Donnell is a debate consultant who trains Republican candidates. He has worked with George W. Bush and John McCain, and for a short time earlier this year, he helped prep Mitt Romney.
O'Donnell is an expert on "the pivot."
If you have watched a debate, you have watched a pivot. "The pivot is a way of taking a question that might be on a specific subject, and moving to answer it on your own terms," O'Donnell says.
(http://www.npr.org/2012/10/03/162103368/how-politicians-get-away-with-dodging-the-question)
Pivoting to answer the question "on your own terms" may result in all kinds of shenanigans: obfuscation, digressing, changing the subject, etc.