When Ann Coulter (poster child for the far right pre-Trump) says Trump is an idiot than it's the mainstream opinion of the non-Trumpet Right Wing. Sure there are a few minor players at Fox trying to back him up but we all saw what happened when Lue Dobbs tried. He got 1.5 words in before being told to STFU (and complying).
It might not be the official corporate view of Fox but it's clearly the prevailing opinion of their viewers. Fox is in free fall, they just sold their entire non-News side of the business to Disney to raise money. They wouldn't go against Trump so ruthlessly unless they knew their viewer base was inline with their thinking.
You have made so many assumptions, it is hard to decide where to start. I don't watch Ann Coulter and rarely hear her name mentioned. I primarily watch The Five, Fox News with Bret Baer, Greg Gutfield and Chris Wallace. I have never heard any of them refer to Trump as an idiot.
I do not like Trump as a person and did not vote for him. I didn't vote for Hilary either. I threw my vote away, but did not think either candidate was presidential material. Trump has a number of characteristics I do not like.
But, anyone who thinks he is a moron or idiot is badly mistaken. Idiots and morons do not become billionaires. He understand business and in spite of the criticism of the tax bill, it appears to have a positive influence.