US Is an Oligarchy Not a Democracy, says Scientific Study

There's considerable empirical evidence from cross-country studies of democracy that limited input and poorly representative government are a product of electoral structures that support duopoly, like the ones that US has had since its founding.

The domination by elites is a result of an electoral process that prevents effective choices (and thus, meaningful input) from coming through the electoral process and drives most meaningful political input through processes other than the formal electoral process.

Constitutional changes focussed on campaign financing rather than fundamental government and elctoral structure are unlikely to seriously change that, though they may redirect the form through which elite influences are directed outside of the electoral process.