In each of the Baltic States, Russia left a large population of Russian people after the east bloc crumbled.  They, themselves, do not regard themselves as Estonians, Lithuanians, or Latvians but they co-exist in mutually beneficial toleration of one another.  Baltic state concern would be that Russia would create ethnic tension and destabilize these states and create a sudetenland scenario.

 It should also be noted that Russian continues to occupy Kaliningrad (Koenigsberg) where they maintain a large naval force to remind Scandinavian neighbours of their dominance of the Baltic  Sea and region.  Remember, how the Russian navy was aggressive towards a naval exercise conducted by western forces earlier this year.  This base gives Russia an ice free port and access to the North Atlantic.

All this should be taken into consideration of Russia recently acquiring a naval base in Syria to establish a presence on the Mediterranean/South Atlantic.  Russia's chess playing causes the distrust.