Should the U.S. still seek to lead the world or should we now focus on problems at home? Should the U.S. still seek to lead the world or should we now focus on problems at home?
I would argue that there is no way that the US can avoid being involved in international affairs today. There is not really any way that the US can disengage from world affairs.
There are two major reasons for this. First, the fact of globalization means that many parts of the world are important to us. The most obvious of these is the Middle East. Problems in that region could seriously cripple our economy and that is something we cannot afford. Second, the rest of the world looks to us. If we pulled back to isolationism, there would be no one to "step up" and take our place as a peacekeeper. This would mean that problems could grow until they became unmanageable. These problems would then impact us.
Since we have been the only superpower for some time now, we are stuck in that position for a while longer. We could try to pull back and let other countries gradually take more responsibility for their own defense, but we cannot simply withdraw all at once from international affairs.
I agree that the two are no longer really separable concepts. The world economy is so fully integrated and inter-dependent, that nation, but especially no industrialized nation, can afford to ignore world events. Where ou energy comes from, who buys America products, the trade routes we depend on, all of these are now permanently integrated on a worldwide scale, and any country that ignores that does so at their own peril.