In the 19th Century, people like Pat Buchanan believed that Catholics and the Irish would never make good Americans.
In the late 19th Century and early 20th Century, writers feared the day when America would no longer be predominantly of "Anglo-Saxon stock" .......And, no, they did not mean the generic "Anglo" of modern P.C. speech. They meant Anglo-Saxon as opposed to German, Irish, French, Italian, Jewish, Scandinavian, Spanish, Polish, Austrian, Greek, Dutch, Portuguese, Russian or anybody else that did not originate from England or Scotland. Somebody with the last name of "Rickenbacker", "Eisenhower" or "Nimitz" was not considered to be of "Anglo-Saxon stock".
How many pure-bred Anglo-Saxon Americans are left in America today outside of remote areas of Appalachia? The only ones that I know are naturalized citizens who still speak with a noticeable British accent.