Kelly hasn’t just gone bad since he hooked up with Trump. He and Trump are of a mind. Kelly is just a much better politician. Here’s a link to an article positing that he’s “always been a hard right bully.” The author uses a 2010 speech by the general to illustrate his contempt for civilians who question war mongering, his paranoid worldview and more. https://theintercept.com/2017/10/21/it-didnt-just-start-now-john-kelly-has-always-been-a-hard-right-bully/
Kelly is truly scary as illustrated by his own words