An atomic bomb would have done the trick... How close were the Germans to the Atomic Bomb? if they hadn't attacked Soviet Union and instead focused of their secret programs, then their dreams of exterminating other races would have got easier (With the loss of living space to radiation).
It seems that Atomic project was very hard to accomplish, from start to finish. Germans made the opening strides, splitting the atom, but couldn't keep up in the race. Also I seem to recall that Heisenberg, either purposely misled the Nazis about necessary critical mass for bomb, or he simply was mistaken. And he was more or less the authority on nuclear matters, on German side.
Clearly Heisenberg was a very smart man, smart scientist and an accomplished one at that. Maybe he was still somewhat out of his field of expertise though, at least a little bit? He wasn't an engineer, a bombmaker. He wasn't a chemist either, or a nuclear expert per sé. (Let's not forget that American effort, a wide team effort of phycisists, chemists and engineers, clearly included a clear goal driven, multifaceted approach) Everything was being explored and done at the same time... results would be seen later. This way some mistakenly chosen path towards bombmaking wouldn't interrupt or ruin success.
It seems that the German problem was more on the practical problem of actually separating the Uranium into the correct isotope, and having figured out how to exactly make the bomb. Americans used up quite a bit of electrical power to separate the natural uranium into weapons grade isotope uranium. This could have become a problem for Germany. Although perhaps Germany may have obtained plutonium, and gone towards that route, although I'm not sure what they would have required in that case.
Germans were among the world leaders in the physics and chemistry fields still at this time, although British and Americans were also up there.
Germany did have enough Uranium mines under its control also. They didn't fund properly their own nuclear research and weapon program, though. It appears only America took it really seriously as a feasible short timeframe project, and Americans really did pour lots of cash into the Manhattan project.