Whatever....
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I guess you could go back to September 1950, the United States created  the Military Assistance Group to screen French requests for 
aid, advise  on strategy, and train Vietnamese soldiers.  By 1954, the US spent  US$1  billion in support of the French military effort, 80  percent of the  cost of the war.
US advisors  present, but not combat troops
Truman was President (D) or
http://tinyurl.com/2ff6f6k
First U.S. Ground Troops Sent to Vietnam
As the fighting between the Viet Cong and the South Vietnamese   continued, the U.S. continued to send additional advisers to South   Vietnam. When the North Vietnamese fired directly upon two U.S. ships in   international waters on August 2 and 4, 1964 (known as the Gulf of   Tonkin Incident), Congress responded with the Gulf of Tonkin Resolution.   This resolution gave the President the authority to escalate U.S.   involvement in Vietnam. 
President Lyndon Johnson used that authority to  order the first U.S. ground troops to Vietnam in March 1965.