He did something much worst then humiliating x or y. Everyone already knew he is a clown, but he pretty much blown any credibility USA still had as a partner for anything, see also tariffs and threatening 2 allies (Canada and Greenland)
This is Don Corleone beheivior, I give you 100 billions in old military equipment and you give me 500 back, really?
Also, USA offered security guarantees on '90s when Ukraine gave back the nukes to Russia. Officials didn't forget that, maybe Trump did.
Ok, then his validation as president was done by the same incompetent old management and it's not valid.
He can say what he wants. International treaties are international treaties. If you break them you loose your credibility, if you still have any after threating to invade your allies.