https://www.brookings.edu/events/the-budapest-memorandum-at-20-the-united-states-ukraine-and-security-assurances/

Pifer claimed that the US implicitly suggested that "lethal military assistance" was the type of support that would be provided.

Also, since all veto-holding members of the UNSC provided similar assurances, it was expected that direct UNSC peacekeeping intervention would be possible. For obvious reasons, it wasn't.