If you read the memorandum text, at most the US promised to go to the UN security council if Ukraine's territorial integrity was threatened.

https://treaties.un.org/doc/Publication/UNTS/Volume%203007/P...

There is a lot of misinformation floating around the internet about this memorandum.

Furthermore, even Wikipedia states: "The Budapest Memorandum is not a treaty, and it does not confer any new legal obligations for signatory states. It was written in a way to avoid an impression of legal obligation."