Bigger then you think.Soviets get A bomb from traitors in 1949,but not plan for bomb which hold it - they do not have agents in Air Forces.There was a narrow window of time during which the USA had nukes and no other country did.
So,they must built it themsleves,and they did - in 1951.
Till 1951 all soviet had was nuclear device that they could blown on land or ship,but not drop from plane.
Which mean,That USA would burn soviet cities till they surrender,and all soviets could do would be burn themselves.
Worst.Americans like Patton saw what should be done,but USA arleady was ruled by Wall Street - and they were soviet friends from beginning.America back then was in many ways too nice and too naive, and we are still paying the price of that naivity.