Never happen. Candidates must be in very general terms and lie on most topics. The main reason is the American public is so ignorant as to where America is now that to elaborate would just be wasting time. It is to the point that a candidate might say he is in favor of no more murders and arsholes would cheer and yell. How, doesn't matter, just the words. Dumb, get it.
You nailed it...American voters are pathetically uninformed.