Here's one take on the behind the scenes power struggle:
"New signs emerged today at just how frantic Ailes has become to get Trump back to the table. The two men have not spoken since yesterday, sources told me. This morning, Joe Scarborough reported that Ailes called Trump's daughter Ivanka and wife, Melania, to get through to the GOP front-runner. But Trump is saying he'll only talk to Rupert Murdoch directly. In a further challenge to Ailes's power, Bill O'Reilly is scheduled to host Trump. Last night, Ailes directed Sean Hannity to cancel Trump's interview. O'Reilly's refusal to abide by a ban adds a new dynamic to the clash of egos. For O'Reilly, this is an opportunity to take back star power from Kelly. Sources say O'Reilly feels he made Kelly's career by promoting her on his show, and he's been furious that Kelly surpassed him in the ratings."
And I admire this theory:
"Perhaps Trump is playing a long-range chess game. He believes that if he is the party nominee he will have to take on the mainstream media, that is, the Liberal Media, in the general election. By taking on Fox now, he establishes a precedent for confrontations in the Fall. It is him against the Media Establishment -- anyone who questions him is "unfair." Also, by his dispute with Fox, he implies for the general election that he is not "in the pocket" of right-wing media."