Dubious Crusade

Dubious - Doubt or uncertainty
Crusade - Any vigorous, aggressive movement for the defense or advancement of an idea.

Warren is trying to show that after we surrendered Saigon to the communists our movement to stop communism and promote democracy was doubtful or uncertain. The citizens of the US were upset and didn't trust the government, and our nation was demoralized. I think this will relate to the study of Vietnam because it shows the impact of the war on the Cold War.