You’re spot on. In the early to mid-1960s Eisenhower stated in interview that US involvement (such as it was) began right after Dien Bien Phu. As a Senator, JFK held or participated in hearings about US involvement in Vietnam, “Lay OS”, etc, keeping up a drumbeat that stopped when he decided to run for President. In his campaign persona, he portrayed Eisenhower as being soft on defense, talked about “brushfire wars”, missile gap, bomber gap, communist takeovers, etc.
The US was largely responsible for Dien Bien Phu itself. After WWII France had no interest in fighting the Viet Minh, and we told them we needed them to do so to contain communism. We funded them and armed them to the teeth; if you see French soldiers in Dien Bien Phu they look like US GIs from 1945 (same gear, helmets, etc.). In a grim foreshadowing of the Bay of Pigs a few years later, promised US air support simply never came.