FOX was just playing the game of poking the stick at the animals.
It was a sort of cheap shot way to start the debate. The same question could have been asked somewhere along the way, and in my opinion been more effective.

Unfortunately all the candidates have predictable hot buttons and the media, all of them, push the one they want when they think it is opportune to do so.....and the candidates know it.....especially Trump, hence he is very easy to goad into a rant (may or may not be a negative!).

I think there was a little too much schtick in the moderators tone last night.