It's pretty simple. The Rus almost certainly have at least some semi-functional nukes (‘semi’ in the sense of H weapons degrading into fission ones because the tritium decayed), and at least some of their delivery systems still work. The liquid fueled ones are probably toast, but that was never a majority of their 'fleet'. No idea on MIRVs or chaff canisters / decoys.

So, it's a matter of not wanting to play actual Russian Roulette with European population centers. To use that metaphor, it’s probably just one round, one corroded round in the cylinder