Setting aside Russia’s own motives, is there any way to take the temperature of Belarus’s own citizens actual preferences around this? I gather their elections have been shoddy for long enough that they’re not a proxy for actual sentiment.

Other than a land grab and closer proximity to Europe - what does Russia gain from this?

Nuclear weapons are all about posturing. Both sides know the consequences of detonation and do everything in their power to avoid it. Thus posturing.

Putin's ego and desire for the old ways.