Everyone should know about the Overton Window

https://en.wikipedia.org/wiki/Overton_window

The Overton window is the range of policies politically acceptable to the mainstream population at a given time. It is also known as the window of discourse.

… basically the idea that political ideas and discourse can be subtly moved from one position to another over time … the danger being that people can be influenced or convinced to move to ever more extreme ideas and policies.