I have listened to Rush since the early 90's. And the 2016 primary season was no different than the rest in that he never endorses a primary candidate. I listen to him typically every week day, generally without fail, and discuss the happenings, as usual, with my wife during my drive home. We would have caught an such change of habit.
He engaged in no "anti-trump screed"
But, I objected with my money and dropped 24/7. As you, I've been listening to Rush forever and I found his rhetoric beyond the pale when it came to the last election.