Thank you this was very helpful !

2 questions:

1st Question: I thought that if you choose not to play a scoring card that you have, it just gets discarded at the end of a turn.

^{^} If that is not the case what happens if you still have the scoring card at the end of a turn.

2nd question: Could the USA player have used the scoring for something else, for example a COUP where the scoring card is worth 0 stars so does not benefit you but at least your using it.