Assuming that Lord Acton’s axiom regarding power and corruption is correct, I think it’s safe to say that the ultimate cause of social corruption in the United States is the individual.
Whenever the state exists, it is axiomatic that someone must hold the power of the state. In a democracy, it is the people that hold the power. Therefore, if corruption occurs, it occurs first among the people. Of course, this does generally turn into a self-reinforcing feedback loop, wherein societal corruption fuels government corruption, which in turn fuels societal corruptions, and so on, ad infinitum.
This begs another question: if power corrupts, how do you undo corruption? In a democracy, corruption is a bottoms-up process that generally concentrates power in the hands of few. Now, is the correction of corruption likewise a bottoms-up process, or should it be a top-down process since that is where the power (and thus corruption) is concentrated?