We have a little bit of a self-vision problem. Historically, America focused on conquering new frontiers: manifest destiny (with all the nastiness that includes), industrialization, the space race, computing. It's not really clear what the next national frontier will be, and a lot of the domestic politics are anchored more around the allocation of resources from past frontiers rather than the establishment of a new frontier. This is all orthogonal to external enemies like the USSR, which I just see as a relatively generic phenomenon; countries frequently unify around external enemies, and you're probably right that the current situation with the USSR won't have a very long-lasting effect.