If a game show that gave away real prizes leaked the questions in advance to one contestant but not the other, that would be fraud. I'm not sure if a debate can be held to that standard, however?

In politics perceptions matter more than reality. Partisans on both sides are quite convinced that the other side's candidate is a criminal.

Democratic partisans believe the other candidate was involved in a criminal conspiracy with foreign powers and/or engaged in criminal conduct to cover it up, and Republican partisans believe that the Wikileaks emails are full of proof of criminal activity by the other side's candidate. (they have probably never actually read any of the emails, but they believe it, which is all that matters)

Neither of those beliefs are strongly supported by evidence but both result from the fact that both candidates have a long history of dubious conduct that their detractors reasonably believe would be criminal if the laws were equally enforced without regard to wealth and political power.