Mussolini had a lot of support from Italy’s Jews, many of whom were very assimilated into Italian ways of thinking. Italy had even had a Jewish Prime Minister before World War I and nobody would have believed that Mussolini, who like Trump is not personally anti-Semitic, would ever turn on them. Some other Italian Jews tried to point out their errors but they were shouted down (in some cases, literally).
History is now repeating itself. Many totally assimilated American Jews, some of whom even keep Shabat and Kashrut and pray three times a day, are supporting Trump. This will not end well.