As it turned out Catholicism in America, suspected from the start of the nation by the Protestants who left Britain because of alleged Catholic tendencies in the Church of England and by Protestants generally, did not finally pose any challenge to American values. Indeed, Catholics became along with other religions as American as apple pie. But why?
In Europe and in Spanish America Catholicism was anti-liberal, intolerant, united with all sorts of reactionary policies, some of which lasted into the mid-20th century. But the Catholic immigrants did not bring this sort of Catholicism with them, nor did most of their priests. Irish and Austrian and French and Eastern European Catholicism never arrived here with its adherents. In fact, at one point in the late 19th century the Vatican condemned what it called "Americanism," a view of religious liberty and separation of church and state not found in historic Catholic nations and not appreciated by the Roman authorities. While "Americanism" as a fictitious heretical doctrine was condemned American immigrant Catholics continued essentially to practice a form of Catholicism never found since the conversion of the Roman Empire to Christianity: a religion of freedom, free thought, and individual liberty.
I think the reason was that the Catholic immigrants approved of American religious freedom and pluralism, something they had never experienced in their homelands, and that they realized despite anti-Catholic prejudices that they encountered owing to the old church-state semi -feudal Catholicism of their homelands was not what made them loyal to the church. They were Catholics in spite of the oppressive history of their church not because of it. Those traditionalist Catholics did not disappear in America, but they were quickly marginalized and by the election of John F. Kennedy no longer in favor. America has gained, Catholics have gained, and the much embattled Roman Church has, despite its denials and obfuscations, gained as well. Freedom is always good -- even for religion and religious people.