One difference between the two might be that the animosity against teh blacks is coming from inside the house, and is so deeply rooted in American history that it can be fairly argued this entire country was founded on racial hatred against people of African features. It’s far more widespread, far more ingrained, and thus far more pernicious than anti-semitism, which comes from outside the house and might be seen as more isolated and transient than racial hatred. In fact, in America, Jews are not even considered a proper race as African-featured people are, while in Europe they traditionally have been considered a race. Jews in America are basically seen as white. That helps tamp down the spread of anti-semitism and thus I don’t believe it will ever reach 20c European proportions here.