“The disaster in Vietnam happened on LBJs watch.”
Not exactly, even though LBJ is deserving of plenty of blame.
The disaster began because of John Kennedy.
In early November 1963 JFK let it be known that he wanted to get rid of Ngo Dinh Diem, South Vietnam’s President. Diem wasn’t compliant enough to suit President Kennedy.
Well the result of this was a coup and the assassination of Diem and his family. This left RSVN leaderless and chaotic, a situation that would persist for years. And just a few weeks later JFK was himself assassinated and Lyndon Johnson had the whole mess dumped in his lap.
Ho Chi Minh could hardly believe his good fortune; Diem was the most effective foe he had of the Communist war against South Vietnam. Now his victim was severely weakened.
In order to bolster a weakened South Vietnam Johnson decided to send in American combat troops, something that both Eisenhower and MacArthur had warned against. And to make that decision even worse Johnson decided to keep control of the war in Washington DC instead of leaving it a military commander, like Ike had been during WWII. The combination of Lyndon Johnson and Robert McNamara insured that the war was fought badly, ineffectively, and at great expense to the GIs sent to fight it.
You are correct about that, but LBJ only compounded the problem.