Throughout medieval and into modern western history, there was always prejudice against people with different religious beliefs. This applied not just to non-Christians, but among different Christian denominations as well. However, in the case of Jews, what I see happening is a transformation from religious to racial prejudice.

From what I can tell, Jews in Europe were viewed as white people who practiced the wrong religion. Benjamin Disraeli's family converted to Christianity when he was ten. Had they not done this, it is unlikely that he would have become prime minister, but his Jewish ancestry did not prevent it. During the 19th century, many Jews converted to Christianity and some changed their last names.

Hitler viewed Jews as a separate race. During the Holocaust, there were people who didn't know they had Jewish ancestors until the Gestapo researched their ancestry and showed up at their door. This sort of racial view of Jews seems to be the prevailing view of anti-semites today.