To what extent did the US lose the Vietnam War on the home front rather than the battlefield?

The two defeats were inextricably linked. The more unpopular the Vietnam War became on the home front the more difficult it was for the United States to bring it to a successful conclusion. So long as opposition to the war was confined to the younger generation, especially college students, the government had little to worry about. But once it spread beyond college campuses, opposition became much harder to ignore.
A growing body of public opinion came to believe that the war had gone on for far too long, taken too many lives, and cost too much money; and all without an obvious exit strategy. Inevitably, the developing mood influenced the political classes, who realized that supporting the Vietnam War was no longer a vote-winner, but rather the exact opposite. Even those Senators and members of Congress who continued to support the war understood the necessity of a way out of a conflict rapidly heading out of control.
Without a sustained level of political support for the war and its original goals there was virtually no chance that the forces on the ground, no matter how numerous or well-equipped, would prevail against their Communist opponents. Long before the last shot had been fired, the United States had effectively lost the Vietnam War on the home front.