Unlike almost every other dominant ethnic, racial or religious group in world history, white Protestants have ceded their socioeconomic power by hewing voluntarily to the values of merit and inclusion, values now shared broadly by Americans of different backgrounds. The decline of the Protestant elite is actually its greatest triumph.
E. Digby Baltzell, a great sociologist about whom I have written before, argued that every society needs a leadership class that assimilates talented individuals who rise from outside the old ruling class. This is hard for the top class to stick to, because it is easier and more comfortable to only promote their own. However, that way lies a caste society and increasing injustice to the talented but excluded. If, though, the leadership class can continue to include talented outsiders, it truly deserves the name of "aristocracy" in the literal sense - the rule of the best.
Baltzell goes beyond other theorists of aristocracy to see that even greater benefit comes to society if these new men (and now women) are included not just in the powerful public institutions, but also in the private world of the leadership class. The acid test of this private inclusion is if the rising individuals marry into the old top class families. If the aristocracies of individuals can solidify into a stable, but porous, network of families, then the leadership class can produce a true Establishment. Their children then are members of the top class by birth and (normally) shared breeding.
I believe Elena Kagan will be a fine Supreme Court justice. I do regret, as a Baltzellian sociologist, that she will not have descendants who can complete the assimilation of this very talented woman into the American Establishment.