As we all know, the Germans had a fairly advanced plan for atomic weapons during WWII. If fate had worked a little differently (part of the reason they came off second was because they expelled a bunch of Jews who then went and worked for the USA inventing the atomic bomb - karma at work lol), they could well have invented a working nuke first - and I'm sure no one needs convincing that they would use it. Now there would have been problems with the delivery system - although they could easily reach the UK and Russia, getting nukes to hit the USA would have been quite a challenge due to the distance. However, let's assume that they manage to find a way to do it - whether high-altitude bombers, long-distance rockets, submarine-launched rockets, or even a secret agent smuggling it in on a cargo ship to somewhere like NYC. Assume that first one, then a second US city gets vaporized by nuclear bombs in 1945, just as happened in Japan. What would have happened next?