PHILLIP LONGMAN is the most important man you’ve never heard of in Washington.

A senior fellow at the liberal New America Foundation, Longman specializes in demography. If you’re a romantic, demography is the science of love, writ large. If you’re a cynic, it is the sausage factory of civilization. Whatever your disposition, demography is, if not destiny, then a subject of paramount importance. In the long run, no weapon, no technology, no economic system is more powerful.