Unitary Rational Actor

One of the assumptions of realist theories in international relations is that states (governments) are unitary rational actors.  This assumption means that states (governments) have one voice in international relations and that they act according to rank ordered preferences of outcomes in so far as possible.  In relation to Cuba the Obama Administration may be breaking away from what many scholars have said is a tendency toward acting in a manner consistent with variants of realist theories of international relations.  According to this article, the administration may break away from Congress in an international forum.  When part of the government acts in a manner different from another part of the same government the unitary actor principle is thrown out the door. 

For my two cents, the Cuban embargo should have ended long ago.  The Cold War is over, in case you neocons and liberal internationalists alike have forgotten.  Opportunities exist to make changes in the world to engage in the meaningful spread of economic and political freedoms in the world.  But if you choke off the ability to engage populations because of Cold War principles, you are cutting off the potential to make real meaningful change in the contemporary world.  What threat to the security of the U.S. population exists from being able to smoke a great Bolivar or Romeo y Julietta while sipping rum on the beach in Cuba?  What threat to our security is represented by allowing U.S. companies to trade in Cuba or Cuban companies to trade in the U.S.?  If you can explain the threat to me, please do so.