We have heard that tenured professors have job security. Awhile ago I posted about the situation of Jonathan Goldstein, whose tenured position at Allegheny College was under attack because he was criticizing his administration. I think his position has been saved, but the hard fact is that administrators succeed in getting rid of uppity faculty all the time, although often it does not get widely reported. Thus, I recently gave a talk at an econ department where someone behaved in a highly and personally aggressive and unpleasant way to me (other members later apologized to me). However, I learned that this was not totally disconnected to the recent firing of a tenured friend of mine from that department for disagreeing with the university administration. I cannot speak further of this because the entire situation is under wraps due to court order. But I can say that my friend was indeed fired for disobeying certain arbitrary administrative rules, the sort of thing that was being thrown at Goldstein, which was simply a method for getting at him for criticizing them on other matters.
At my university there was an effort to fire a tenured prof who was criticizing the administration by eliminating his entire department. This led to a protest against this, which I was involved with. Some of us involved in this received letters from a member of the Board of Visitors above the administration, threatening us with loss of our jobs. Fortunately, this move to eliminate the department was ultimately countermanded, and the administrator causing the trouble was removed as a result of his connection with a murder/prostitution scandal. But I still keep a copy of that threatening letter in my desk, not to mention my membership in the AAUP current.