[lenerdenator]

That, and cultural.

Irish-Americans are less ambivalent about their roots than many other people of European descent - being excited about being part-German in Missouri is tantamount to being excited about watching paint dry, for example - and the fact that a man of Irish descent was President of the United States within two centuries of the "famine" and after centuries of oppression by the English boosts the credibility of America as a "land of opportunity", even if only in retrospect.