Principle, rigor and execution matter in US foreign policy

First of two parts

US President Barack Obama has come under intense criticism for his foreign policy, along with many other things. This is not unprecedented. Former President George W. Bush was similarly attacked. Stratfor has always maintained that the behavior of nations has much to do with the impersonal forces driving it, and little to do with the leaders who are currently passing through office. To what extent should American presidents be held accountable for events in the world, and what should they be held accountable for?