I think after questioning (yes, quite fairly) Perry’s IQ, Trump has a little less moral high ground to stand on here.
Perry was calling Trump everything in the book, including a cancer on the GOP. I guess Donald did question the intelligence of a former Texas governor who could maintain with a straight face that the illegal problem was not just as Donald said it was. Donald has certainly been vindicated as the facts come out. Perry was out of line and still is.
I think the question in each of these cases, is who strikes first. Once the candidate or their surrogate hit low, the resulting punch back is twice as hard. Perry went after Trump, and the result was strong.
It’s an interesting and unique campaign approach, but it’s clear he’s going back hard and swiftly when someone gets nasty towards him.