The other thing to remember is this... if the US isolates itself, does this mean that all of it's businesses will also take part?
Three off the top of my head:
MacDonald's
Coca-Cola
Microsoft
These corporations have businesses in every continent (maybe with the exception of Antarctica). They represent the USA as much as they do global capitalism.
While I would find it very interesting to see the US pull it's military back to it's borders, it should be noted that the main reason they are there to begin with has little to do with protecting the homefront, and everything to do with protecting it's economic interests.
Again, I suggest you check out this link for a complete history of all American battles on foreign soil:
LINK. The vast majority have everything to do with protecting US economic interests.
The US has never really been isolationist rather they tried to stay out of other people's business as long as it didn't interfere with theirs.