The options he has are not good at all.

He can try to disable military support Ukraine is getting by attacking transports before they reach Ukraine.

He might try to intimidate the West by dropping a small nuclear bomb on a strategically important place in Poland. Then, he could say that the big bombs would fall on London, Berlin, and Paris if the military help to Ukraine continued.

I wrote about that two months after the war started; would not write it differently today.