It's on the use of tactical weapons? Okay.
There's a military and an alliance component here. For the military component, it's not clear what Russia would even gain militarily by using a tactical nuclear weapon in terms of the situation on the battlefield.
The political effect of basically breaking the taboo for the first time since 1945 would be enormous. Now, enormous in terms of the reaction of NATO.... Radoslaw Sikorski has been very explicit about what NATO would apparently do. It's basically a complete, massive, conventional attack on any Russian positions in legal Ukrainian territory. Also, in terms of Russian alliances, there are not that many. They're relatively isolated.
The one thing that China has said that is not inclined towards Russia since the beginning of the war is “don't do it”. They've said that publicly and it's on their peace plan that dates from February 2023. It's don't use nuclear weapons. Of course, they use different diplomatic language, but the message was very clear.
The military gain is questionable. The military cost might be huge coming from NATO. Then the diplomatic cost to that alliance and, therefore, also to supply chains—a lot is coming from China that has dual use—might be too high for the Russians.
That would be my understanding.