We already put the world on notice regarding our response to agression while we are heavily committed in another theater.
Remember the big brou-haha about our nuclear weapons usage Report?
Screw with us while we are vulnerable and the response will be devastating - I don't think anyone doubts this.
This is a bit off-topic, but I wonder how the world economy would react if there were to be a brief and limited nuclear exchange, either involving us or between two countries like India and Pakistan. Even if no U.S. cities were to be involved, I have to think that the stock market would drop a lot harder than it did post 9/11, and there might even be a run on the banks from the panic and fear of another nuclear exchange. One thing is certain....we live in interesting times.