American Political System

[Vladimir]

Are those individual congressmen and interest groups totally independent from any kind of influence of those two major powers ?

I don't want to sound rude but of course not. The issue is the level of influence and if any laws are broken. Granted, alot of the influence is likely interpersonal and difficult to document.

Duverger's Law. Majoritarian electoral systems trend towards a two-party system.

I haven't heard of this. I thought it was more down to tradition.

The current US system creates red versus blue states. 150 years ago that led to a civil war. Where is the moderation in that?

This was due to economics and not politics even though the Democrats came to dominate the south; and 150 years ago is hardly current.