On the February night that the right-wing writer Milo Yiannopoulos was scheduled to speak at the University of California, Berkeley, thousands of protesters showed up wearing bandannas and masks covering their faces. Their identities a secret from the police, some in the crowd turned violent and set fires.

Mr. Yiannopoulos’s speech was canceled, and, until Wednesday morning, the authorities at Berkeley were preparing for what could have been an even larger demonstration over the visit of another polarizing figure, Ann Coulter. The conservative media personality, who has said she would speak Thursday, canceled her appearance after the conservative groups that had initially sponsored her backed out because of safety concerns.

Some conservative media sites have criticized the University of California for not cracking down on protesters from the left, and have lauded the tough stance taken by the authorities at Auburn University in Alabama. Before a speech by the white nationalist Richard Spencer at the Auburn campus last week, the police stopped anti-fascist protesters and ordered them to remove their masks.