The Vietnam stab-in-the-back myth asserts that the United States' defeat in the Vietnam War was caused by various American groups, such as civilian policymakers, the media, anti-war 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 in World War I. Unlike the German myth, the American variant lacks an antisemitic aspect. Jeffrey Kimball wrote that the United States' defeat "produced a powerful myth of betrayal that was analogous to the archetypal Dolchstoss legend of post-World War I Germany".
The myth was a "stronger version of the argument that antiwar protest encouraged the enemy, suggested that the antiwar movement might in the end commit the ultimate act of treachery, causing the loss of an otherwise winnable war".
Similar accusations have been made throughout US history.
During the War of 1812, the War Hawks accused supporters of the Federalist Party in New England of "near-treasonous activity" for failing to conquer Canada.
Right-wing commentators also claimed that US President Franklin D. Roosevelt had "sold out" Second Polish Republic Poland and the Republic of China had the Yalta Agreement and blamed US President Harry S. Truman and US Secretary of State Dean Acheson for American failures during the Korean War.
Casualties mounted slowly during the Vietnam War after the 1965 deployment of combat troops and in 1968 surpassed those of the Korean War.
During the war, hearings were held in the US Senate regarding the progress of the war. At hearings of the Senate Preparedness Investigating Subcommittee (SPIS), generals testified that the failure of the war in 1967 was caused by excessive civilian restraint on target selection during the bombing of North Vietnam, which the subcommittee agreed with. Joseph A. Fry contends that the Joint Chiefs of Staff and SPIS, by blaming the media and antiwar protesters for misrepresenting the war, cultivated the stab-in-the-back myth.
Although much of the American public had never supported the war, General William Westmoreland blamed the American media for turning the country against the war after the 1968 Tet Offensive. That narrative was followed by later writers such as Guenter Lewy and Norman Podhoretz. One study estimated that until the offensive, American pundits supported their government's war policy four to one and afterward, they switched to being two to one against it. Many history textbooks state that the offensive was followed by public opinion turning against the war, and some accounts mention media coverage. Another element of the myth relates to the 1973 Paris Peace Accords in which the stab-in-the-back interpretation holds that obstruction in Congress prevented the United States from enforcing the accords. According to Lien-Hang T. Nguyen, that interpretation of the accords has "more or less been rejected by most scholars in the field," but it is alive in popular discourse.
In 1978 and 1979, Nixon and Kissinger respectively published best-selling memoirs based on access to still-classified documents that suppressed the decent interval theory and "prop[ped] up the Dolchstoßlegende," according to the historian Ken Hughes.
In 1982, Harry G. Summers Jr. wrote that the idea that internal forces caused the defeat in Vietnam was "one of the more simplistic explanations for our failure... this evasion is rare among Army officers. A stab-in-the-back syndrome never developed after Vietnam." However, according to Ben Buley, Summers' book is actually one of the most significant exponents of the myth although Summers proposes a more subtle version in which the military is criticized, but the primary responsibility for the defeat lies with civilian policymakers.
In his 1998 book, The Spitting Image: Myth, Memory, and the Legacy of Vietnam, Jerry Lembcke compared the stab-in-the-back myth with the myth that returning veterans were spat upon by and insulted by antiwar protesters, but no spitting incident has ever been proven to have occurred. According to Lembcke, the stab-in-the-back myth was more popular during the war, and the spitting myth gained prominence only in the 1980s. In his 2001 book The Culture of Defeat: On National Trauma, Mourning, and Recovery, Wolfgang Schivelbusch denied the existence of a Vietnam stab-in-the-back myth comparable to the German one. Although he wrote that some US rhetoric was "quite similar to that voiced by right-wing Germans during the Weimar Republic," he argued that the Vietnam War "did not entail national collapse,.... was not followed by a humiliation like that of the Versailles Treaty.... [and] did not polarize the nation or lead to civil war". Jeffrey Kimball wrote that Schivelbusch "was incorrect on virtually every count."
Kimball writes that the stab-in-the-back charge was resurrected in the 2004 United States presidential election as the Democratic presidential candidate, John Kerry, was criticized for opposing the war after he had returned from Vietnam. In 2004, Charles Krauthammer wrote in The New Republic that broadcaster Walter Cronkite had caused the US to be defeated: "Once said to be lost, it was." In 2017, David Mikics wrote that "the Vietnam stab-in-the-back argument is now largely dead."
Moyar’s critique shows that a line of argument that Jeffrey Kimball long ago called the 'stab-in-the-back legend' remains alive and well. The stab-in-the-back legend displays classic characteristics of what psychologists call in-group/out-group bias, in which every action by an in-group is rationalized and justified whereas every action by an out-group is criticized and seen as inspired by perverse motives. Through this pattern of thought, the 'stab-in-the-back' interpretation externalizes blame for U.S. defeat entirely to civilian policymakers. A virtuous and effective military had its hands tied by villainous civilians who, pandering to base political instincts, betrayed the soldiers (and eventually South Vietnam) by failing to allow them to do what was needed to win.
Finally, the Administration suggested a stab-in-the-back theory of the war. This stronger version of the argument that antiwar protest encouraged the enemy, suggested that the antiwar movement might in the end commit the ultimate act of treachery, causing the loss of an otherwise winnable war.