Actually, it was his predecessor, Kennedy, who started it. LBJ simply carried on, then escalated that conflict.
When I was an Army brat in the early 60s, my dad was already training for that mission. He got his first orders to deploy there in 1964.
As I said, I don’t know all that much. Still, neither of them received flak for dragging America into it. At least, nothing compared to the amount of flak our soldiers got for fighting it.