Blaming Truman for the Viet Nam War seems a bit much.

French-Indo China (later North and South Vietnam) was still French until after the Battle of Dien Bien Phu and the signing of the Geneva Peace Accords in 1954.

https://en.wikipedia.org/wiki/Battle_of_Dien_Bien_Phu

Every single President since at least FDR has hidden war aims and actions from the US people.