Final answer:
The release of the Pentagon Papers in 1971, demonstrating the U.S. government's deceit regarding the Vietnam War, significantly eroded public support for the conflict. Along with the Tet Offensive and the My Lai Massacre, these revelations contributed to widespread anti-war sentiment and disillusionment with the government.
Step-by-step explanation:
An event that significantly turned public opinion against U.S. involvement in the Vietnam War was the revelation of the Pentagon Papers in June 1971. These classified documents exposed the U.S. government's misrepresentation of the military's role and ability to win the war. They disclosed that the government had misinformed the public and Congress about the intensity of the war, the progress being made, and the likelihood of success.
Additional factors that contributed to the shift in public opinion included the Tet Offensive, a series of disastrous surprise attacks by North Vietnamese forces, and the report of the My Lai Massacre, which exposed the brutality of the conflict and led to international outrage. These elements, coupled with ongoing antiwar protests, eroded the public's trust in the government and led to a dramatic decrease in support for the war effort.
The growing anti-war sentiment represented a deep division in American society between the hawks, who supported the war, and the doves, who opposed it. Despite initial support, the persistent coverage of the war's harsh realities in the media and the understanding of the war's apparent unwinnability led to increased protests and a sense of disillusionment among the American public. By the time President Nixon announced the withdrawal from the quagmire, only a minority of the population continued to support the Vietnam War.