The main difference is that the societies are different. Hitler presided over a nationalist militaristic imperial society called "Germany" that had a fanatical devotion toward its leaders. US politicians preside over a money-loving society that does not even want a government or a leader. Sure; we have our share of militaristic nuts, Christian nuts, and many other groups. But we don't really have a dominant group in our democracy other than the libertarian money-lovers (who are astonishingly ignored by the political parties). The political parties sort of bring the other various groups together under umbrellas, which causes our politicians to have to placate those within the party embrace. But politicians are cut from the same cloth. They all crave power. You could put Hitler in the US as president or move FDR to be leader of Germany. It probably would not make a difference.