Russia cannot lose Belarus after losing the Baltics and Ukraine. Germany is today a liberal democracy with little military power. So was Germany in 1932. Things change.
But a Russia poised inside Belarus is a terrible threat to NATO states Estonia, Latvia, Lithuania--especially to any NATO forces sent there--and Poland; as well as being a threat to Ukraine.
Nor can Russia's even justifiable fear be a license for Russia to control its neighbors. Where does that end?
Understanding Russia's fears is valid right up to the point that Russia uses that fear to justify conquering unwilling subjects.
UPDATE: And let me add that after the collapse of the Soviet empire from 1980-1991, NATO tried to balance Russian fears and the rights of countries to forge their own path.
While NATO expanded into former Soviet vassal states who requested NATO membership, NATO left those new members a void of NATO troops and logistics infrastructure-or even plans to defend the new frontier.
Heck, at one point America withdrew its last tank from Europe! Even Russia's invasion of Georgia in 2008 didn't end that military void in the east. The Obama administration attempted a glorious "Reset" with Russia!
It took Russia's 2014 invasion of Ukraine and repeated threats to Europeans--including nuclear weapons threats--to get NATO to take defending its new members seriously.
Bravo Russia. Will nobody in Russia tell Putin he is effing up royally?