What he will have to come to grips with is if he's dismayed Trump has hung on this long and may capture the republican nomination, that he bears a lot of the responsibility for not calling Trump a populist. It was fun while Trump kept Bush, Christy and others from achieving the nomination. But I think he's realizing the fun is ending and there's now a reality to be dealt with.
He knows that, and knew that. Plus "populists" is a very general term. it's basically everyone without a recognized political philosophy. Not that this is a bad thing, it's just a position where self interest and terms like best, better, OK, not so good, and bad, actually mean something politically.
The people who don't know that are the GOP.
There is also a large contingent of people who consider themselves (self identification) as "Conservatives" but in reality they hold a few conservative positions and don't get into the philosophy of Conservatism.
Back in the day we called these people republicans. Over the years efforts were made to pigeon hole the republican base, but a lot of folks don't fit in any defined hole.
There was a time when I did not either. I called myself a Republican. Today, because I have studied and absorbed the philosophy of Conservatism, I now call myself a Conservative.
None of this is new, but it might be new for some who really don't understand how they actually fit politically and are now forced by circumstance (Trump) to do something they have never done before and that is to look inside and do a analysis.