It can happen here. Thinking it can’t is how it does. Hitler’s rise to power wasn’t totally legal either, and people thought it was impossible… and yet it happened.

This isn’t to say it will happen, but it can happen. He doesn’t need an amendment. That’s only required if you pretend like rules and norms are the only way things get done. They’re only as useful as the people willing to stand against him when he breaks them are. If people aren’t ready to stop him then there’s no limits.