Would Einstein, Bohr, Fermi, and the rest have ended up in the USA if the war in Europe had not started until several years later?
No. Delaying rearmament doesn't delay the Nuremberg Laws or the implementation of the rest of the Nazis' anti-semitic agenda inside Germany.
Also, about the men you mentioned. Einstein had no involvement in the Manhattan Project beyond signing a letter written by others which alerted FDR to the prospect of a Nazi Bomb. Bohr famously got his estimate for critical mass wrong and, because of the way the Nazis had setup science in the Reich, there was no one how could challenge him about that mistake. [edit - Please see footnote] While Fermi's work with "atomic piles" was critical (no pun intended) for the production of fissionables, he worked on the Project as a general consultant and then primarily at Hanford. Like Einstein, it was felt having Fermi "disappear" behind the security veil drawn over Los Alamos would be too much of a red flag.
Seeing as Germany won't be occupying Poland, the Holocaust there and elsewhere in Eastern Europe will be delayed, but the Holocaust had already begun inside Germany in the 1930s. The Wannsee Conference "merely" expanded and industrialized a process which was already occurring.if the Reich is not at war until, let's split the difference and say in 1943 instead of in 1939, would the Holocaust been delayed? If so, then would "Jew Science" still be held in such contempt that all that could flee, would flee?
No. Italy is too poor to develop the industrial plant necessary for fissionable production. We often talk about how mismatched Japan was against the US. Well, during this period Italy ranked below Japan in industrial capacity.IIRC in 1938 when Fermi received the Nobel Prize in Stockholm, he, his wife Laura, and their children emigrated to New York. This was mainly because of the new laws promulgated by the regime of Mussolini in order to bring Italian Fascism ideologically closer to German Nazism. Could Italy have developed the A-Bomb first if Fermi had stayed in Italy?
Italy couldn't even afford to build the tanks it needed, so finding a spare 2 billion in 1940 USD will be impossible. And that's just the Bomb too. I often point out the need for a delivery system too. The US spent more on developing the B-29 than it did on the Manhattan Project.
Footnote - I stupidly and inexcusably confused Bohr with Heisenberg. Bohr isn't going to leave Europe without a German occupation of Denmark. However, seeing Bohr in the OTL didn't leave until '43, his presence or lack thereof won't effect a UK or US nuclear project.
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