In what ways might the change in the makeup of the American population affect the American social, political, and economic landscape?
When you talk about “the change” in the makeup of our population, I assume that you are talking about the fact that our population is aging and become less white. It is very hard to know what impacts this will have on the various “landscapes” that you ask about.
The clearest impact, or so it would seem from our current vantage point, is on politics. It seems obvious that the United States is going to become less conservative and less Republican unless something changes. So far, at least, the Republican Party is having a very hard time reaching out to non-whites and, to some degree, to younger white people. Their current base will erode further and they will struggle unless they can manage to appeal more to nonwhites.
The economic and social impacts will be less clear. I would argue that the social impact will be minimal. Most children and grandchildren of immigrants will be essentially identical to other Americans except in skin color. Even that will change as there will be more intermarriage. The basic underlying American culture will assimilate the nonwhite immigrants and, especially, their descendants.
Economically, the major problem is likely to come from the aging of the population. We will have more people on Social Security and Medicare and fewer people to earn money to support them. This will be a serious problem unless something is done. The changing racial/ethnic face of the country should not really have that much of an impact on economics.