I feel they were biased in another, more insidious way (and they went along with it). Trump has carefully crafter a persona for himself over the years (perhaps even accidentally, by virtue of his personality), where he can pretty much say anything (and especially things no other candidate would ever be able to say without saying goodbye to any chance at election), and the media (and people) will just go "oh, well, sure he said some racist, sexist things, but that's just Trump... you know how he is". Kind of like that racist uncle at the dinner table... you gotta put up with it, but at least he's family, so you understand him better, and perhaps realize he has other redeeming qualities.

So, this has allowed Trump to appeal to bases of people no other candidate could even hope to reach, with the current "acceptable" rhetoric.