First, Fox’s promotion of Trump worked too well. He went from making the Republican primary more interesting to follow — and thus better for ratings — to dominating the Republican primary and potentially harming the ideological movement that Fox supports. Murdoch’s public opposition to Trump was a signal that the network wasn’t likely to tolerate Trump actually becoming the Republican nominee.

Second, Trump had spent much of his time in the hackier corners of the network — outposts of conservative inanity like Fox and Friends. But the debate was led by Fox’s more serious personalities. Baier, Kelly, and Wallace want to be known as some of the toughest questioners in news business — and Trump was a chance to prove their journalistic bona fides to the world. So where other Fox personalities wanted to treat Trump well in the hopes he would come back on their shows, Baier, Kelly, and Wallace wanted to embarrass Trump.

Finally, Fox News’s incentives had switched. Early in the campaign, the way to get bigger ratings was to build Trump up. But now the whole country was tuning in, and what most people wanted to see was Trump torn down — or at least the fight that would result if Fox News tried to tear Trump down. And that’s what they got. It was extraordinary television, and it led Fox to the highest ratings for any cable news program ever broadcast. Fox figured out how to profit off Trump coming and going, and, better yet, they got to decide when Trump was coming and when Trump was going.

Now Trump and Fox News are at war. And, as Nate Silver writes, this is a war Trump probably can’t win.