The Budapest Memorandum was signed by Bill Clinton, John Major, Boris Yeltsin and Leonid Kuchma – the then-rulers of the USA, UK, Russia and Ukraine - as part of the denuclearization of former Soviet republics after the dissolution of the Soviet Union
Technically it means that if Russia has invaded Ukraine then it would be difficult for the US and Britain to avoid going to war.
http://www.freerepublic.com/focus/f-news/3128111/posts
“The Budapest Memorandum was signed by Bill Clinton...”
Presidents can sign anything they want, but unless the Senate approves, the treaty doesn’t mean squat.