US colleges confront a new era of sometimes-violent protest

FILE - In this Feb. 1, 2017, file photo, University of California, Berkeley police guard the building where Breitbart News editor Milo Yiannopoulos was to speak in Berkeley, Calif. UC Berkeley police took a hands-off approach to protesters on the campus when violent rioters overtook a largely peaceful protest against a controversial speaker. After a series of protests around the country, some institutions are rethinking their security and tactics in an age of growing political polarization. (AP Photo/Ben Margot, File) (The Associated Press)

FILE - In this March 2, 2017, file photo, Middlebury College students turn their backs to author Charles Murray during his lecture in Middlebury, Vt. After a series of protests around the country, some institutions are rethinking their security and tactics in an age of growing political polarization. (AP Photo/Lisa Rathke, File) (The Associated Press)

After protests turned violent at several college campuses in recent months, some colleges and universities are wondering if they'll be next.

Some campus police are trying new tactics to try to keep events peaceful. Other schools have abruptly canceled controversial speakers over safety concerns, as the University of California, Berkeley, did with conservative writer Ann Coulter.

Police from about 40 schools took part in protest preparation and response trainings in March in California, Indiana and Maryland. Another session takes place Thursday at the University of Hartford in Connecticut.

At Vermont's Middlebury College in March, protesters shouted down a guest speaker. A professor was injured in a melee afterward.

The previous month at Berkeley, three people were arrested in a protest that stopped a speech of a right-wing commentator. Six people were injured.