Question In a bi-cameral, two-party, district responsive legislature can it be effective in a world that is drastically changed from a time when the Constitution was written.
Is Congress responsive to what is best for the nation at a time when the US is a single super-power in the world?
Answer You are actually asking two questions. Is it effective, and is it responsive to what is best for the nation?
It is still reasonably effective. The "checks and balances" system created by the Constitution still works as long as the two Parties have relative parity. If one Party controls all three sections of government, then there could be some problems.
As for doing what is best for the nation, that question is always asked of representatives in a Republic form of government. Do they do what is best for the nation, or for themselves? I would answer that individual members act according to their own interests. If it is in their interests to reflect their constituents, or do what is best for the nation, then they will. If it is not in their interests, then they won't. There hasn't been many examples of representatives standing up against their constituents because of the greater good.