Vietnam stab-in-the-back myth
The Vietnam stab-in-the-back myth asserts that the United States' defeat during the Vietnam War was caused by various American groups, such as civilian policymakers, the mass media, antiwar protesters, the United States Congress, or political liberals. Used primarily by right-wing war hawks, the name "stab-in-the-back" is analogous to the German stab-in-the-back myth, which claims that internal forces caused the German defeat during World War I. However, the American claim usually lacks the antisemitic elements, implicit or express, of its German namesake.
Source: Wikipedia — Vietnam stab-in-the-back myth (CC BY-SA 4.0)