The decision to send Lenin to Russia, (remember, the Original Russian revolution was not communist. When Lenin got there, he turned it into a communist revolution.) was made after the US announced it was entering the war on the side of the British.
I know post hoc ergo propter hoc is not perfect logic, but it seems accurate in this particular case.
And why would it mean no nuclear weapons?
No German loss in WWI, no Hitler. No Hitler, no mass persecution of the Jews. Szilard remains in Germany, as do a whole host of other important scientists that pushed for and developed this technology.
No Szilard and Einstein in the US, no push to create the Manhattan project.
Very likely the very wost things of the 20th century would have been avoided.
The first Russian Revolution happened a month before the US entered the war. The Germans would have let Lenin go back to Russia anyway, whatever the US did because it would effectively take Russia out of the war.
If the war continued, as is likely, there could well have been a Bolshevik Revolution in Russia. What would happen next is impossible to say. Maybe Communist Russia is crushed by Germany. Maybe Communist Russia inspires or incites revolution in Germany or France or Italy. Maybe war continues in the East between Communists and anti-Communists. At any event, there would be plenty of chaos and atrocities.
No German loss in WWI, no Hitler. No Hitler, no mass persecution of the Jews. Szilard remains in Germany, as do a whole host of other important scientists that pushed for and developed this technology.
So the Germans would get the bomb. Or the Russians. Or the Japanese. The idea that only a handful of exiled scientists could have done it at only a narrow window of time is nonsensical. Any great power sufficiently devoted to create nuclear weapons would eventually have them once the science was worked out.
In general, the idea that if you stop something from happening at one time then it would never happen at another time and under other circumstances doesn't always pan out. There may be underlying forces at work that will produce the same result at a different time. Or a technology not discovered at one point may be discovered later on and produce similar effects.