I posed this question because: The U.S. is a republic. This we all know.
But we provide many Social Services to the population. Our roads, police and fire protection, our defense, social security, the recent corporate bailout; are all examples of "Socialist principals". Our taxes pay for our "collective society" and they are for the benefit of us all.
A better definition of the United States is: We are a Social Republic, and through the democratic process we choose our elected representatives; while practicing capitalist economic theory.