Dee, the
Budapest Agreement of 1994 had 4 signers:
Russian Federation
Ukraine
United States of America
United Kingdom of Great Britain and Northern Ireland
Basically, if one wants to stick to the absolute strictest definitions in that Article, then those 3 nations have an obligation to join Ukraine in it's defense.
Question is what do you do if Ukraine needs defense from any one of those 3?
From my perspective, the Russian Federation walked all over Section 3 in 2012 with it's customs embargo against Ukraine, then did the same to Section 2 in 2014 with
the annexation of Crimea.
From where I stand, anything Ukraine has done against Russia after that, said agreement could be used in its defense.
Similarly, any actions by the US and the UK on the side of Ukraine against the offender could also be used as a justifiable and contractual intervention.
( to the likes of Crickets and Scotts of PM, I did say "could" and not "should"