Ted Cruze makes it clear :
Hard questions Baaaaad
Easy questions Gooood
It isn’t hard or easy, it is personal attacks/gotcha or policy discussion. They can save the gotcha’s for the one on one interview. A debate is so we can see their policies side by side and hear relevant discussion.
The moderators failed, they asked bad questions, took too much time asking those bad questions and were more interested in how they were doing than in providing a forum for the candidates.