The way i see this as i know what kind of person is Lindsay Graham my friend done business with him long time Ago , so i can say that this person never forget betrayel zelensky told him to make deal, so now Lindsay Graham can take legal action and arrest warrant could be issued then they can Do all the investigation where is all the money.
In this world it's easy to take money because law enforcement agencies and Anti money laundering agencies working fast all over the world and evem russia will cooperate with USA if there is order from USA law enforcement as Putin is also with law enforcement background and he respect laws.
Btw, USA specially the Lindsay Graham want money definately they get it.