The secretary of Miami-Dade County’s Republican Party started a group chat primarily for conservative students last fall — and within three weeks it was filled with racist slurs, someone wrote dozens of ways of violently killing Black people and the chat was renamed after what one member described as “Nazi heaven.” In WhatsApp conversations leaked to the Miami Herald, participants used variations of the n-word more than 400 times, regularly described women as “whores,” used slurs to talk about Jewish and gay people and mused about Hitler’s politics. Interspersed throughout were discussions about events promoting the Republican Party at Florida...