Many of the incidents that occurred around the Vietnam War could be referred to as “turning points”. Included in this list is the coup against Diem, the 1963 assassination of President Kennedy, the Gulf of Tonkin resolution, 1963 Buddhist riots, and the 1964 United States Presidential elections. In addition, the attack on the U.S.S. Maddox in 1964 was also a turning point for America’s involvement in the war.
On August 2, 1964, the Maddox’s radar detected five patrol boats. “When the boats were less than 10,000 yards away, the destroyer fired three shots across the bow of the lead vessel.” (Andrade & Conboy,1999) In response, the North Vietnam boat launched a torpedo. The Maddox fired again, this time to kill, and hit the second North Vietnam boat just as it launched two torpedoes. Badly damaged, the boat hobbled home. On August 4, 1964, the U.S.S. Turner Joy and the Maddox believed they were again the subjects of attacks by patrol boats from North Vietnam. It is believed today, that these attacks did not in fact occur and they were reports from jittery radar and sonar operators (Andrade & Conboy, 1999). These were considered to be the first two attacks by the North Vietnamese against the U.S. For this reason it would be considered a major turning point in the conflict.
These attacks by the North Vietnamese against the U.S. boats was the first intentional act of violence against the U.S.. America responded to this by creating the Gulf of Tonkin resolution. This resolution stated “Congress approves and supports the determination of the President as Commander-in-Chief, to take all necessary measures to repel any armed attacks against the forces of the United States and to prevent further aggression. The United States is therefore prepared, as the President determines, to take all necessary steps, including the use of armed force, to assist any member or protocol state of the Southeast Asia Collective Defense Treaty requesting assistance in defense of it’s freedom” (Moss, 2010, p. 134). That prepared the U.S. to act on attacks should they occur.
The events leading up to the Gulf of Tonkin Incidents such as the coup against the Diems could have led the North Vietnamese to believe that the South Vietnamese and the U.S. had been weakened, vulnerable to an attack and more likely to lose. The point at which this became a turning point in the war was when the U.S. fought back. After the Gulf of Tonkin incidents, the North Vietnamese bombed AVRN forces and U.S personnel in Saigon. The U.S. was forced to react to this and attack. This became the first true military attack in the war.
The Gulf of Tonkin incidents were the first intentional attacks against the U.S. As a result of this, the U.S could no longer provide just aid to the Vietnamese. We had to fight back As far as American involvement in the Vietnam War; this was considered a turning point.

References:

Andrade, D., & Conboy, K. (1999). The secret side of the Tonkin Gulf incident. Naval History, 13(4), 27.

Moss, G.D., (2010). Vietnam :An American Ordeal, (6th ed.) Upper Saddle River, NJ: Prentice Hall