Those moderators aren't liberals -- they're morons. You can be stupid and weak-willed without being on the left side of the political spectrum, you know. The fact that your man is still above water in polling (though that should begin to change) is proof of this.
The moderator who unsuccessfully tried to debate Trump over whether the debate was supposed to run 3 hours, John Harwood, is a well-known Twitter lefty who always defends Hillary. He's a true liberal, and had no business moderating a GOP debate.