The moment you see it. People will call you crazy, and and an alarmist, and hyperbolic, but it's your duty to call it out and to keep calling it out from the moment you recognize it until it goes away. And don't let anyone tell you you're wrong, because the number one tool of fascists is plausible deniability. They thrive on Hanlon's razor. The love to play in a gray zone, to get you upset, and then to say "you're overreacting" when you call them out for exactly what they're doing. Don't fall for it.