He never directly spoke against a third term, just “violating the constitution”, and then named some enemies. It’s a long way off still, but you can see the groundwork being laid for something like “emergency measures to protect the constitution” if they decide that’s the way they want to go.
Really, it's just an "if enough people in power and in general go along with it, then it works" kind of thing. The current trend in the GOP is to whip and/or expel those who do not fully support Trump. What happens if half of the elected politicians, most of their constituents, and most of the appointed government officials, decide that Trump is staying in office? No one knows. The power of words on paper only goes as far as people let it.
https://en.wikipedia.org/wiki/United_States_Electoral_Colleg...
Any examples?
If you don't take his threats seriously by now, and the willingness of the GOP to get behind whatever he wants, then you are not paying attention - it has happened over, and over, and over.