What is the author's tone in A Vietcong Memoir: An Inside Account of the Vietnam War and Its Aftermath by Truong Nhu Tang?

The overall tone of the story ranges from excitement and optimistic to one of foreboding and despair. When Tang realizes he has spent the majority of his life working for a cause, and that those he helped put in power are self-serving and unwilling to create a true coalition government, Tang is filled with despair. Knowing he is unable to go on fighting, he gives up and leaves the country aboard a boat.