Powers writes in The Daily Beast: (HT: mh)
The root of nearly every free-speech infringement on campuses across the country is that someone—almost always a liberal—has been offended or has sniffed out a potential offense in the making. Then, the silencing campaign begins. The offender must be punished, not just for justice’s sake, but also to send the message to anyone else on campus that should he or she stray off the leftist script, they too might find themselves investigated, harassed, ostracized, or even expelled. If the illiberal left can preemptively silence opposing speakers or opposing groups— such as getting a speech or event canceled, or denying campus recognition for a group—even better.
Read the whole article. I assume it serves as a good introduction to her new book The Silencing: How the Left is Killing Free Speech.