The other one is about 300 sqkm with 5 million people.
When in doubt, use basic logic.
Your argument is the same as Iraq being a realistic threat against the US.
Also, list of Russian neighbors not threatened or invaded by Russia:
Belarus (pushed into a sort of union state)
China (too big)
Japan (I think)
Mongolia (I think)
Azerbaijan (I think)
List of neighbors threatened or invaded by Russia:
Ukraine
Georgia
Moldova (Transnistria occupied since 1991)
Estonia
Latvia
Lithuania
Finland
Poland