To see how federalism would look if Puerto Rico were admitted as a state, we need only examine our neighbor to the north, Canada.
In most respects, Canadians are just like Americans: a majority-English-speaking, majority-Protestant people living in a collection of former British colonies. The exception to the rule is Quebec. When Canada began the gradual process of securing independence from the United Kingdom, federalism was seen as the only way to unite the English-speaking Protestant provinces with the French-speaking Catholic one. And while the differences between Catholic and Protestant are less important to most people nowadays, the differences between French- and English-speaking Canadians remain and have helped preserve the federal nature of Canada’s union when other centralizing, progressive trends in Canadian politics might have destroyed it.
Even when Canada’s government is to the left of ours, federalism is maintained, with foreign affairs and economic policy mostly handled in Ottawa and cultural and educational matters dealt with at the provincial level. We think of Canada and the U.K. as both having socialized health care, and that’s true. But the two systems are not managed the same way. Britain’s National Health Service is the sort of top-down model that conservatives in this country fear; Canada’s model is managed by the provinces, not unlike our Medicare system. Both systems would probably entail too much government intrusion for most Americans, but the Canadian version offers more local control, and works better, than Britain’s.