The conversation between Russell & LBJ is indeed interesting, but note that it is a conversation about a situation they have been plunged into by decisions not their own. They are discussing how to "get out" of that situation, not the situation itself.
The conversations that would throw light on the situation occurred after Dien Ben Phu between John Foster Dulles & President Eisenhower -- and their chief advisors. That was when the key decisions were made, and if you want to analyze how the U.S. 'elite' makes major decisions, that is what you need to analyze.
Carrol