[dead]

You're right, LBJ was the third president to send US personnel to Vietnam. I think JFK was the first to send troops.

[vbmoneyspender]

JFK was the one who turned Vietnam into a real problem. After JFK signed off on the assassination of Diem, Cambodia's leader, Prince Sihanouk, decided that it might not be such a prudent thing to have a president like JFK as an ally. As a result, Sihanouk ordered all U.S. advisors out of Cambodia and declared Cambodia to be a neutral state in the fight between North and South Vietnam. This directly led to the creation of the Ho Chi Minh trail which kept North Vietnam's southern proxies supplied through think and thin and materially expanded the scope of the war.

[Still Thinking]

You're right, LBJ was the third president to send US personnel to Vietnam. I think JFK was the first to send troops.

Either JFK wasn't the first, or LBJ wasn't the third, unless you're counting the phantom president that came between.