About the only scenario where this *might* be possible is something like my A Sound of Thunder where the Soviets use their secretive M-I Complex, hijack German nuclear physicists *and* their spies in Tube Alloys to make their Bomb in a few years as much for Stalin's ego as for anything else. Even then the Soviets have until the USA gets the Bomb to enjoy their
monopoly, and they have no means to sustain a lead in nuclear technology for any length of time.