Another thing I haven't seen mentioned is that Stalin and Churchill were very aware that the US had the Atomic bomb and IOTL Truman even asked their approval/opinion if he should use it on Japan (Which essentially debunks the whole "Revisionist" theory that the US dropped the atomic to "intimidate" the Soviets"), and I can definitely see them not only be very confused if whoever occupied the white house at the time was just sitting on this knockout weapon but putting a tremendous amount of pressure on whoever was president to use it as they would be losing soldiers every day and would be getting super pissed that the US was just chilling on this weapon. (I know Stalin doesn't really care about his men in the military from a humanistic point of view but was facing man power shortages so from at least a strategic point of view doesn't want to lose a bunch more soldiers.)