By this rationale, the Jews are just as responsible for the rise of Hitler since many wealthy Jews invested heavily in Germany, as well.
The story line on Prescott Bush is that like a lot of Americans (see the Dem favorite Averill Harriman) they invested in German operations before the Nazi threat was known and kind of got stuck there as the political climate changed. I don't see how his grandfather's investment is worse than Joseph Kennedy's actively flacking for the Nazis once the threat was known and he was serving as our Ambassador to England, do you?
It's just a nasty bit of business to spin.