Well, Stalin didn’t fear the nukes. After all, USA only had 2 at that time, and no ICBMs that time, so USA still had to launch the bombs. Good luck launching them in key places as Stalingrad or Moscow, soviets had much more planes than Japan when Hiro and Nagasaki, and you have to travel a long run. Maybe they could nuke Leningrad with some good spy work (confusing soviets about the place where the nuke is dropped), but that was of no use after how germans left the poor city
There were more problems: soviet land army had gross numerical advantage, T-series where far better than allied tanks and you can guess political ramifications in places where commies had some force as China, Greece, Italy and even France. You have to explain USA’s public opininio why attack a former allie that didn’t attack first, etc. No walk in the park, just more kills and not clear victory. Truman did well not attacking, Patton only wanted the glory
But as fantay scenario, 1947 is better after chinese civil war is done. Allies vs soviets and chineses, a fair 4 players scenario