Not only because the U.S.A. didn't walk out victorious from that conflict, but also because in the 60s there were multiple undergoing circumstances inside the country simultaneously.
That moment in time shifted the country morally, culturally, socially, politically and economically; in spite of being a foreign dispute, it fostered domestic revolt altering the American character at its core, to the point of been labeled as the worst foreign policy calamity in history. Hence "The Vietnam War" was an extensive turning point in the United States.