What is the root problem in US politics?

It's not hard to find evidence that the effectiveness and approval of the US political system is at an all-time low for a united country (i.e., leaving out the civil war). Is there some issue that is at the root of this? Some reform or change that would make things start to work better? Obviously, I'm not asking for miracles; nothing is going to satisfy everyone. I'm just saying that a system which is satisfying basically no one, when it used to be a model for the world, clearly needs fixing. How?