I have been using that label for Trump supporters for months - didn't even know Hume used it. It is short-hand so I don't have to write "Trump supporters" over and over again. If you want to refer to me as a "Cruzer", feel free. And if you want to get offended by the term "Trumpkin", you are free to do that as well. I have noticed that many Trump supporters get offended by just about as many things as the SJW college students do...
Megyn Kelly and Brit Hume affair background:
http://gotnews.com/megyn-kelly-affair-fox-newss-research-division-and-the-loving-the-party-problem/