As an elite, Jews don't really behave much differently from rich people. They form cliques, but they are discriminating, why should they help out another Jew that does not benefit them personally? There is a bias, but it is not strong. The same with WASPs who will gladly hire a Jew in place of their useless cousin.

Regardless, because of their lower level nepotism and historical social darwinism, Jews are an elite group in America, like the WASPs. Where maybe 10% of Irish are upper-middle class, about 50% of Jews are, and naturally Jews are "overrepresented" by similar proportions in elite institutions.