Already the California Highway Patrol is heavily Mexican.(At least in our area.) Local police Departments are slowly becoming Mexican.
Soon California courts will conduct proceedings in Spanish(no law has yet been passed requiring this.)
In short "Gradualism."
At some point “gradualism” becomes “sudden”. Kinda like that Russian flag mysteriously appearing over a Crimean government building, and lots of unidentified armed strangers in cammo killing anyone who seemed to resist the implications.