In this timeline, the Soviets are the first to develop and test atomic bombs, developing them before Hitler stabs them in the back; unbeknownst to the world of the USSR's great accomplishment. How would World War II and the world be different?
I usually get annoyed by people who instantly say "ASB!", but this time I have to agree. Even if all prominent physicists move to the Soviet Union rather than the US, there's no way they can make a nuke before Barbarossa.