"Illegal alien" is one of the greatest accomplishments of language engineering and was unambiguously successful.

When the left tries this today it results in equal and opposite backlash and has no effect in terms of policy, winning elections, and that sort of stuff, but it certainly can be a motor that keeps online bubbles bubbling.

Again, I think this is likely seen differently depending on which side of the political spectrum one stands, and what sources of information one attunes to. I agree that both 'racism' and 'gender' have become flash-points for discord, and that one can point to the left as trying to change the definitions. But I can think of other words that the right is equally guilty of attempting to re-define. For example, 'woke' was a term originally rooted in African American communities meaning awareness of systemic injustice, but is now used by the right as pejorative for anything they disagree with. (Including the existence of systemic injustice, sigh.)